Provide user friendly message.

bt5/erp5_credential/SkinTemplateItem/portal_skins/erp5_credential/ERP5Site_viewNewCredentialRequestDialog/your_reference.xml

@@ -16,6 +16,14 @@
               </list>
             </value>
         </item>
+        <item>
+            <key> <string>delegated_message_list</string> </key>
+            <value>
+              <list>
+                <string>external_validator_failed</string>
+              </list>
+            </value>
+        </item>
         <item>
             <key> <string>id</string> </key>
             <value> <string>your_reference</string> </value>
@@ -26,7 +34,7 @@
               <dictionary>
                 <item>
                     <key> <string>external_validator_failed</string> </key>
-                    <value> <string>The input failed the external validator.</string> </value>
+                    <value> <string>Selected login is already in use, please choose different one.</string> </value>
                 </item>
               </dictionary>
             </value>

bt5/erp5_credential/bt/revision

-363
\ No newline at end of file
+364
\ No newline at end of file