--- a/vApp12/frontend/preview/vApp12.js
+++ b/vApp12/frontend/preview/vApp12.js
@@ -72,6 +72,7 @@
             url: backend+"/users",
             data: obj,
             success: function(data) { location.reload(true); },
+            error: function(e) { alert(e); },
             contentType: "application/json",
             dataType: 'json'
         });