Been getting this error for over a week now and it's starting to get old. I have completely deleted and re-downloaded Creation Kit, I have re-verified the files, and I have renamed my ClientRegistry.blob and got a new one. None of that has fixed it, done a Google search to see if I could find any other solution, but I see now. Any ideas here?

I had it happen to me.

Did you use the uninstall option in Steam? Doing that - and reinstalling, fixed it for me