As of Jan 14th 2016 , this problem still exist.
I just upgraded Windows UI from the Telerik Control Panel, and then when I open my project I get an the same error Value cannot be null. Parameter name: instance.
After a while, I solved it by just selecting the Telerik Upgrade Wizard option in Visual Studio. Deleting the .resx file was not necessary and only led to file not found.
I would like to know is this something we have to do every time there is a upgrade?