This may happen for several reasons.
Make sure that you are working with the latest Revit version
You can also check which action caused this error and try to rectify it. You can share here what happens before the error appears and we can help.
Mostafa Elashmawy
Did you find this post helpful? Feel free to Like this post.
Did your question get successfully answered? Then click on the ACCEPT SOLUTION button.
you can try to refer to this LINK and see if helps. thanks
A bit more info would be helpful, there are a bunch of things that could cause this...
I think the most common cause of that error that I've had experience with was down to the Site Designer plug-in, older versions can cause issues. Check if you've got it installed and check if it's updated, or alternatively remove it.
Sie finden nicht, was Sie suchen? Fragen Sie die Community oder teilen Sie Ihr Wissen mit anderen.