Attached image shows the error displayed in the XAML designer for each and every Telerik control in the entire solution. The error occurred after I added a new WPF Custom Control Library to the solution which I have since removed. How do I resolve this?
1) check your reference paths
2) delete the obj folder(s) and build the solution again. (learned that hard way working with xaml and mysterious errors)
Deleting the obj folders didn't help, but when I checked the reference paths for Telerik assemblies I discovered a couple of dll's that were pointing to a location buried deep within my AppData folder. Removing and then re-adding the correct reference resolved the issue.