Any idea what causes this error?
I keep running into this problem with one of our projects. It has only happened in this one project. I think it might have something to do with the fact that we are on 2007, and one of the other companies working on the project is in 2005.
As near as I can tell, everything was fine until I got one of their drawings, and XREF'd it into my base file. My base file had a topology created in 2007, and their file had a topology created in 2005. Now I've got this problem. I got it cleaned up once already by basically recreating every DWG in my plan set by creating new DWG files from our template, and then querying all data out of the old DWGs and into the new, and then copying all layouts from the old DWGs to the new. It was rather annoying, but it fixed everything for a while. Now the problem is back again.