Big stick time if it is, but I'm just guessing from what you've told me.
I would ideally like more than one file to test if I'm going to write something to get rid of this issue, however, having said that, it might not be the cause of your opening problem...but should still be fixed.
One thing I drummed into people when I taught AutoCAD was the difference between Attach and Overlay and that I almost always prefer Overlay, except in very specific circumstances and only then, if the users knew the consequences.