While working successfully in Visual Studio I suddenly encountered the error message in the subject line when I tried opening an existing WinForm that inherits the DexUIForm. Now, when trying to open any existing forms with that inheritance or if I try to create a new Microsoft Dynamics GP Form I receive that message. I found this previous link that apparently resolved the issue years ago but it did not resolve it for me.
I have uninstalled/reinstalled the Microsoft Dynamics GP Project and Item Templates for Visual Studio addin (VSIX package built by Tim Wappat). I have restored the Development Server to before the issue and uninstalled/reinstalled the addin again...all to no avail.
The full message is shown below. Thank you for any assistance.