The Logs are stored in App_Data\Sitefinity\Logs. Make sure to clear it before reproducing the error.
Also can you try and login to your website and reproduce the issue- then attach the trace log ( or give us a link to it)
and send it to me so I can have a closer look at the service exceptions.
Please make sure that the widget classes are properly referring to existing files.
the Telerik team
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