Hi Telerik!
I spent lots of time investigating the following situation.
For some reason the editor that I used to modify Telerik.ReportDesigner.exe.config file switched xml elements names to lowercase.
ReportDesigner was not started at all in that case. Even no error message was shown.
I had to explore system events logs and found that ReportDesigner.exe throwed an System.IO.FileLoadException.
But still with no details.
Only after hours of exploring I found the problem with xml-element names and fixed it.
I think if you add .config file validation with user-friendly messages during ReportDesigner starting it will help.