Is that the only message you get? Are there any other popups? Also, is there an extra message printed in the Rhino command line / command history?
Solved it. I went to C:\Users\[user name]\AppData\Roaming\McNeel\Rhinoceros\5.0\Plug-ins. There were two DIVA folders, I deleted the older one, and it appears to work now.
Hmm -- thanks Elliot. Good to know that could be a problem. My troubleshooting would not have brought us there!
Happy to contribute to the body of knowledge as I am seemingly expert at generating errors! (see numerous contributions to this forum)