diff --git a/plugins/stoa/controllers/stoa_plugin_controller.rb b/plugins/stoa/controllers/stoa_plugin_controller.rb
index ad68c07..1db6803 100644
--- a/plugins/stoa/controllers/stoa_plugin_controller.rb
+++ b/plugins/stoa/controllers/stoa_plugin_controller.rb
@@ -25,7 +25,11 @@ class StoaPluginController < PublicController
   end
 
   def check_usp_id
-    render :text => { :exists => StoaPlugin::UspUser.exists?(params[:usp_id]) }.to_json
+    begin
+      render :text => { :exists => StoaPlugin::UspUser.exists?(params[:usp_id]) }.to_json
+    rescue Exception => exception
+      render :text => { :exists => false, :error => {:message => exception.to_s, :backtrace => exception.backtrace} }.to_json
+    end
   end
 
 end
diff --git a/plugins/stoa/lib/stoa_plugin.rb b/plugins/stoa/lib/stoa_plugin.rb
index d75239a..9da2b87 100644
--- a/plugins/stoa/lib/stoa_plugin.rb
+++ b/plugins/stoa/lib/stoa_plugin.rb
@@ -31,9 +31,16 @@ class StoaPlugin < Noosfero::Plugin
             function(data){
               if(data.exists) jQuery(me).removeClass('checking').addClass('validated');
               else jQuery(me).removeClass('checking').addClass('invalid');
+              if(data.error) displayValidationUspIdError(data.error);
             }
           );
         });
+
+        function displayValidationUspIdError(error){
+          jQuery.colorbox({html: '<h2>'+error.message+'</h2>'+error.backtrace.join("<br />"),
+                           height: "80%",
+                           width:  "70%" });
+        }
         EOF
       )
     }
diff --git a/public/stylesheets/application.css b/public/stylesheets/application.css
index 4358483..12f8244 100644
--- a/public/stylesheets/application.css
+++ b/public/stylesheets/application.css
@@ -6548,7 +6548,9 @@ h1#agenda-title {
 #signup-form #user_password,
 #signup-form #user_password_confirmation,
 #signup-form .filled-in,
-#signup-form .passwords_match {
+#signup-form .passwords_match,
+#signup-form .invalid,
+#signup-form .checking {
   border-width: 2px;
   border-style: solid;
   background-color: #fff;
@@ -6626,6 +6628,8 @@ h1#agenda-title {
 }
 
 #signup-form span.invalid {
+  border: none;
+  padding: 0px;
   background: transparent;
   color: #FFA000;
 }
@@ -6636,6 +6640,8 @@ h1#agenda-title {
 }
 
 #signup-form span.checking {
+  border: none;
+  padding: 0px;
   background: transparent;
   color: #4A4A4A;
 }
--
libgit2 0.21.2