diff --git a/inc/myco.js b/inc/myco.js
index b4cb6bb..2525f05 100644
--- a/inc/myco.js
+++ b/inc/myco.js
@@ -93,13 +93,13 @@ view_home=function() {
     balances=groups.balances();
     var sum=0;
     for (g in balances) {
-      if (jQuery.type(balances[g]['balance'][user.name])!='undefined') {
-        if (balances[g]['balance'][user.name]['diff']<0) {
-          sum+=balances[g]['balance'][user.name]['diff'];
-          diff='<td class="negative">'+balances[g]['balance'][user.name]['diff'].toFixed(2)+'</td>';
+      if (jQuery.type(balances[g]['balance'][user.email])!='undefined') {
+        if (balances[g]['balance'][user.email]['diff']<0) {
+          sum+=balances[g]['balance'][user.email]['diff'];
+          diff='<td class="negative">'+balances[g]['balance'][user.email]['diff'].toFixed(2)+'</td>';
         }
         else {
-          value=balances[g]['balance'][user.name]['total']-balances[g]['min'];
+          value=balances[g]['balance'][user.email]['total']-balances[g]['min'];
           sum+=value;
           diff='<td class="positive">+'+value.toFixed(2)+' €</td>';
         }
@@ -143,9 +143,9 @@ set_contributors=function(group) {
     $('#view-group #contributor').append('<option>Aucun participant</option>');
   }
   else {
-    $(group.contributors).each(function(idx,c) {
-      $('#view-group #contributor').append('<option value="'+c.name+'">'+c.name+'</option>');
-    });
+    for (email in group.contributors) {
+      $('#view-group #contributor').append('<option value="'+email+'">'+group.contributors[email].name+'</option>');
+    }
   }
 }
 
@@ -153,11 +153,11 @@ on_contributor_change=function(e) {
   show_contributions(groups[$('#view-group').data('uuid')],$('#view-group #contributor')[0].value);
 }
 
-show_contributions=function(group,contributor_name) {
+show_contributions=function(group,contributor_email) {
   var tbody=$($('#view-group #contributions tbody')[0]);
   tbody.html('');
   total=$($('#view-group #total-value')[0]);
-  contributions=group.contributionsByContributorName(contributor_name);
+  contributions=group.contributionsByContributorEmail(contributor_email);
   contributions.reverse();
   if (contributions.length==0) {
     tbody.append('<tr><td colspan=3>Aucune contributions</td></tr>');
@@ -185,6 +185,7 @@ on_click_add_contributor_btn=function() {
   $($('#add_contributor_modal h4')[0]).html('Ajouter un participant');
   $($('#add_contributor_modal #add_contributor_submit')[0]).html('Ajouter');
   $('#view-group #edit_id')[0].value='-1';
+  $('#add_contributor_modal #add_contributor_email').attr('disabled',false);
   $('#add_contributor_modal').modal('show');
 }
 
@@ -201,18 +202,13 @@ on_valid_add_contributor_modal=function(e) {
     alert('Vous devez saisir un nom !');
     return;
   }
-  duplicate=group.contributorByName(name);
-  if (duplicate!=undefined && duplicate.id!=edit_id) {
-    alert('Un contributor porte déjà ce nom !');
-    return;
-  }
   var email=$('#add_contributor_email')[0].value;
   if (email=='') {
     alert('Vous devez saisir un email !');
     return;
   }
   duplicate=group.contributorByEmail(email)
-  if (duplicate!=undefined && duplicate.id!=edit_id) {
+  if (duplicate!=undefined && edit=='-1') {
     alert('Un contributor utilise déjà cet email !');
     return;
   }
@@ -220,12 +216,10 @@ on_valid_add_contributor_modal=function(e) {
     group.addContributor(new Contributor(name,email));
   }
   else {
-    group.replaceContributor(edit_id,new Contributor(name,email));
+    group.replaceContributor(email,new Contributor(name,email));
   }
   set_contributors(group);
   $('#add_contributor_modal').modal('hide');
-  $('#add_contributor_name')[0].value='';
-  $('#add_contributor_email')[0].value='';
   groups.save();
 }
 
@@ -237,11 +231,12 @@ on_close_add_contributor_modal=function () {
 on_edit_contributor_btn_click=function(e) {
   var group=groups[$('#view-group').data('uuid')];
   $('#add_contributor_modal').data('group-uuid',group.uuid);
-  contributor_name=$('#view-group #contributor')[0].value;
-  contributor=group.contributorByName(contributor_name);
-  $('#view-group #edit_id')[0].value=contributor.id;
+  contributor_email=$('#view-group #contributor')[0].value;
+  contributor=group.contributorByEmail(contributor_email);
+  $('#view-group #edit_id')[0].value=contributor_email;
   $('#add_contributor_modal #add_contributor_name')[0].value=contributor.name;
   $('#add_contributor_modal #add_contributor_email')[0].value=contributor.email;
+  $('#add_contributor_modal #add_contributor_email').attr('disabled',true);
   $($('#add_contributor_modal h4')[0]).html('Editer un participant');
   $($('#add_contributor_modal #add_contributor_submit')[0]).html('Valider');
   $('#add_contributor_modal').modal('show');
@@ -264,12 +259,8 @@ on_confirm_del_contributor=function(contributor) {
  * Add/edit/delete contribution
  ********************************/
 on_show_add_contribution_modal=function(e) {
-  var cs=$($('#add_contribution_modal #add_contribution_contributor_name')[0]);
-  cs.html('');
-  $('#view-group #contributor option').each(function(idx,option) {
-    cs.append($(option).clone());
-  });
-  cs[0].value = $('#view-group #contributor')[0].value;
+  $('#add_contribution_modal #add_contribution_contributor_email').html($('#view-group #contributor').html());
+  $('#add_contribution_modal #add_contribution_contributor_email')[0].value=$('#view-group #contributor')[0].value;
   $('#add_contribution_modal #add_contribution_title').focus();
 }
 
@@ -284,8 +275,8 @@ on_click_add_contribution_btn=function() {
 on_valid_add_contribution_modal=function(e) {
   e.preventDefault();
   var group=groups[$('#add_contribution_modal').data('group-uuid')];
-  var contributor_name=$('#add_contribution_contributor_name')[0].value;
-  var contributor=group.contributorByName(contributor_name);
+  var contributor_email=$('#add_contribution_contributor_email')[0].value;
+  var contributor=group.contributorByEmail(contributor_email);
   if (contributor==undefined) {
     alert('Participant inconu !');
     return;
@@ -333,7 +324,7 @@ on_valid_add_contribution_modal=function(e) {
     contribution_uuid=$('#add_contribution_modal #edit_uuid')[0].value;
     group.updateContribution(contribution_uuid,new Contribution(contributor,cost,title,date));
   }
-  show_contributions(group,contributor_name);
+  show_contributions(group,contributor_email);
   $('#add_contribution_modal').modal('hide');
   $('#add_contribution_modal form')[0].reset();
   groups.save();
@@ -363,7 +354,7 @@ on_contribution_edit_btn_click=function(e) {
   $($('#add_contribution_modal #add_contribution_submit')[0]).html('Valider');
   contribution_uuid=$($(e.target).parents('div')[0]).data('uuid');
   contribution=group.contributions[contribution_uuid];
-  $('#add_contribution_modal #add_contribution_contributor_name')[0].value=contribution.contributor.name;
+  $('#add_contribution_modal #add_contribution_contributor_email')[0].value=contribution.contributor.email;
   $('#add_contribution_modal #add_contribution_title')[0].value=contribution.getTitle();
   $('#add_contribution_modal #add_contribution_cost')[0].value=contribution.cost;
   $('#add_contribution_modal #add_contribution_date')[0].value=moment(contribution.date).format('DD/MM/YYYY');
@@ -406,7 +397,7 @@ display_balance=function(group) {
     else {
       diff='<td><span class="glyphicon glyphicon-thumbs-up"></span></td>';
     }
-    tbody.append('<tr><td>'+c+'</td><td>'+bal['balance'][c]['total'].toFixed(2)+' €</td>'+diff+'</tr>');
+    tbody.append('<tr><td>'+bal['balance'][c]['name']+'</td><td>'+bal['balance'][c]['total'].toFixed(2)+' €</td>'+diff+'</tr>');
   }
   $('#display_balance_modal #total-value').html(bal.sum.toFixed(2)+' €');
   $('#display_balance_modal').modal('show');
@@ -523,28 +514,33 @@ on_click_sync_btn=function(e) {
   navbar_collapse_hide();
   if (user) {
     pleaseWaitShow();
-    sync_server.sync(user.server, user.email, user.password, groups.export(),
-      function(data) {
-        console.log(data);
-        if (data.groups) {
-          groups.import(data.groups);
-          groups.save();
-          refresh_group_list();
-          pleaseWaitHide();
-          alert('Groupes synchronisés');
-        }
-        else {
-          pleaseWaitHide();
-          console.log(data);
-          alert('Erreur durant la synchronisation :(');
-        }
-      },
-      function(data) {
+    onsuccess=function(data) {
+      console.log(data);
+      if (data.groups) {
+        groups.import(data.groups);
+        groups.save();
+        refresh_group_list();
         pleaseWaitHide();
-        console.log(data);
-        alert('Impossible de contacter le serveur :(');
+        alert('Groupes synchronisés');
       }
-    );
+      else {
+        onerror(data);
+      }
+    }
+    onerror=function(data) {
+      pleaseWaitHide();
+      console.log(data);
+      if (jQuery.type(data['loginerror'])!='undefined') {
+        alert(data['loginerror']);
+      }
+      else if (jQuery.type(data['syncerror'])!='undefined') {
+        alert(data['syncerror']);
+      }
+      else {
+        alert('Erreur durant la synchronisation :(');
+      }
+    }
+    sync_server.sync(user.server, user.email, user.password, groups.export(),onsuccess,onerror);
   }
   else {
     alert("Vous devez vous connecter pour commencer");
diff --git a/inc/myco_objects.js b/inc/myco_objects.js
index 9e6206f..e628885 100644
--- a/inc/myco_objects.js
+++ b/inc/myco_objects.js
@@ -116,7 +116,7 @@ function GroupList() {
 function Group(uuid,name,data) {
   this.uuid=uuid || generate_uuid();
   this.name=name || false;
-  this.contributors=[];
+  this.contributors={};
   this.contributions={};
   this.deletedContributions={};
 
@@ -126,9 +126,9 @@ function Group(uuid,name,data) {
   }
 
   this.export=function() {
-    var contributors=[];
-    for (idx in this.contributors) {
-      contributors.push(this.contributors[idx].export());
+    var contributors={};
+    for (email in this.contributors) {
+      contributors[email]=this.contributors[email].export();
     }
     var contributions={}
     for (uuid in this.contributions) {
@@ -147,42 +147,39 @@ function Group(uuid,name,data) {
    * Contributors
    */
   this.removeContributor=function(c) {
-    this.contributors=this.contributors.filter(function(v){
-      return (v.name!=c);
-    });
+    delete this.contributors[c.email];
   }
 
   this.contributorByName=function(name) {
-    for (c in this.contributors) {
-      if (this.contributors[c].name == name) return this.contributors[c];
+    for (email in this.contributors) {
+      if (this.contributors[email].name == name) return this.contributors[email];
     }
     return undefined;
   }
 
   this.contributorByEmail=function(email) {
-    for (c in this.contributors) {
-      if (this.contributors[c].email == email) return this.contributors[c];
+    if (jQuery.type(this.contributors[email])!='undefined') {
+      return this.contributors[email];
     }
     return undefined;
   }
 
   this.addContributor=function(c) {
-    c.id=this.contributors.length;
-    this.contributors.push(c);
+    this.contributors[c.email]=c;
   }
 
-  this.replaceContributor=function(idx,c) {
-    c.id=idx;
-    this.contributors[idx]=c;
+  this.replaceContributor=function(email,c) {
+    delete this.contributors[email];
+    this.contributors[c.email]=c;
   }
 
   /*
    * Contributions
    */
-  this.contributionsByContributorName=function(name) {
+  this.contributionsByContributorEmail=function(email) {
     var ret=[];
     for (uuid in this.contributions) {
-      if (this.contributions[uuid].contributor.name==name) {
+      if (this.contributions[uuid].contributor.email==email) {
         ret.push(this.contributions[uuid]);
       }
     }
@@ -223,10 +220,9 @@ function Group(uuid,name,data) {
     total={}
     min=-1;
     max=0;
-    for (idx in this.contributors) {
+    for (email in this.contributors) {
       var sum=0;
-      c=this.contributors[idx].name;
-      cl=this.contributionsByContributorName(c);
+      cl=this.contributionsByContributorEmail(email);
       for (idx in cl) {
         sum+=cl[idx].cost;
       }
@@ -236,16 +232,17 @@ function Group(uuid,name,data) {
       if(max<sum) {
         max=sum;
       }
-      total[c]=sum;
+      total[email]=sum;
     }
     balance={}
     var sum=0;
-    for (c in total) {
-      balance[c]={
-        'total': total[c],
-        'diff': total[c]-max,
+    for (email in total) {
+      balance[email]={
+        'name': this.contributors[email].name,
+        'total': total[email],
+        'diff': total[email]-max,
       }
-      sum=sum+total[c];
+      sum=sum+total[email];
     }
     return {
       'balance': balance,
@@ -262,19 +259,18 @@ function Group(uuid,name,data) {
     try {
       this.uuid=data.uuid;
       this.name=data.name;
-      if (jQuery.type(data.contributors) == 'array') {
-        for (idx in data.contributors) {
-          this.contributors.push(new Contributor(
-            decodeURIComponent(data.contributors[idx].name),
-            decodeURIComponent(data.contributors[idx].email),
-            idx
-          ));
+      if (jQuery.type(data.contributors) == 'object') {
+        for (email in data.contributors) {
+          this.contributors[email]=new Contributor(
+            decodeURIComponent(data.contributors[email].name),
+            data.contributors[email].email
+          );
         }
       }
       if (jQuery.type(data.contributions) == 'object') {
         for (uuid in data.contributions) {
           this.contributions[uuid]=new Contribution(
-            this.contributorByName(data.contributions[uuid].contributor),
+            this.contributorByEmail(data.contributions[uuid].contributor),
             data.contributions[uuid].cost,
             decodeURIComponent(data.contributions[uuid].title),
             data.contributions[uuid].date,
@@ -295,14 +291,13 @@ function Group(uuid,name,data) {
   }
 }
 
-function Contributor(name,email,id) {
+function Contributor(name,email) {
   this.name=name;
   this.email=email;
-  this.id=id;
   this.export=function() {
     return {
       'name': encodeURIComponent(this.name),
-      'email': encodeURIComponent(this.email)
+      'email': this.email
     };
   }
 }
@@ -319,7 +314,7 @@ function Contribution(contributor,cost,title,date,uuid,lastChange) {
   this.lastChange=lastChange || new Date().getTime();
   this.export=function() {
     return {
-      'contributor': encodeURIComponent(this.contributor.name),
+      'contributor': this.contributor.email,
       'uuid': this.uuid,
       'cost': this.cost,
       'title': encodeURIComponent(this.title),
diff --git a/index.html b/index.html
index b0fc0d2..5007e67 100644
--- a/index.html
+++ b/index.html
@@ -316,7 +316,7 @@ body{
           <div class="form-group">
             <div class="input-group">
               <span class="input-group-addon">Participant *</span>
-              <select id='add_contribution_contributor_name' class="form-control"></select>
+              <select id='add_contribution_contributor_email' class="form-control"></select>
             </div>
           </div>
           <div class="form-group">