Unhandled exception => NullReferenceException
I got Type "xxxx" cannot be resolved. error when I try to add my custom widget into my page. Then I found a solution in your posts. I have changed ToolboxesConfig.config file under /App_Data/Sitefinity/Configuration/ (Removed line about my widget) but now i cannot access to my project's administration page. Application returns me "Unhandled exception => NullReferenceException" error message and shut down. I've revoked my process but nothing's changed. By the way I'm using Sitefinity 5.4 version. Thanks for helping.
I am sorry to hear about the problems you are encountering, but is it possible to provide us with some screenshots of the actual errors you get as the messages you get are a bit general and its hard to pinpoint the exact problem.
If you are getting an error about a specific type not being resolved correctly, that means that either the registration of the widget is not correct ( the host type ) or the widget does not exist in the solution. If you however make a change to the Toolboxes config at some point, make sure to restart the application so that the changes can be taken into consideration.
Let us know if you can provide some screenshots of the problems that you encounter.
the Telerik team
I just restarted my computer and problem solved. Thats it :)