We upgraded our DNN site to 9.10.2. The upgrade completed without a problem in both test and then production environments, and the Telerik removal process outlined here also went smoothly on test. But, when I attempted to repeat the same process in production, Step 10 broke our site, generating a server error complaining that the Telerik control were missing and rendering further action through the CMS impossible. Had to roll back to our backup and try again, but the same thing happened. 

I figured out that I could manually copy the backed-up Telerik DLL files back in to "fix" the issue, but then of course we're back at Step 10 again and as soon as they're once again removed, site breaks. Also, I noticed something fishy when comparing test vs. production--the Digital Asset Management module is still listed under Installed Extensions on production, even though I deleted it including "all files" in step 8. It's listed as an installed module but the delete icon no longer appears next to it and the DigialAssets folder is no longer present under /DesktopModules. I wonder if this is culprit, but if it is I have no idea how to fix. 

Any and all advice on this would be much appreciated!