Does it do it with all drawings, or just one? You can do an audit on the drawing and tell it to automatically fix errors. Sometimes that helps. This happened to me once before and the audit didn't fix anything. I ended up starting a new drawing and then copying the old into it and loaded the layout tabs as well. This seemed to fix it for me, but that's the only way that I found.

Are they old drawings that were originated from an earlier version? I was asking around a bit yesterday and someone mentioned that she had problems from time to time with older drawings.