class not registered

Sounds like you either installed a corrupted version of WB, sometimes a download process can corrupt a file if there are network issues. Seems unlikely to me, but I suppose that it ca happen on rare occasions. More likely there may be a conflict between Windowblinds and another piece of software on your system, and the conflict is creating that issue and popup.

Have you tried just shutting down the pc, and then rebooting up again? Sometimes just a shutdown and reboot can help....

If not, please try this: Here the steps on Windowblinds purge and reinstall 

https://forums.stardock.com/486023/windowblinds-support-faq#reinstalling.

Again, just to make sure re-download latest Windowblinds from your account. Reboot after the purge. Reinstall Windowblinds. Reboot again after the installation. Retest to see if the problem still there.

Report back here and let us know if you are still having issues! 

That seems to have worked.  Thank you.

I'll edit the fact that it worked.  It didn't.  I followed the instructions above, and thought it had worked.  But when I went to close out windows explorer it wouldn't even close.  I had to shut the computer completely off.

Hello,
Sorry to hear you are having issues. Need to know more on your system.

1. You on Windows 10 or 11?
2. Need it full version/build number. Please use Winver.exe.
3. If you uninstall Windowblinds, reboot and test do you have issues with your Windows explorer?

Thank you..
Basj,
Stardock Community Assistant.