gui won't open in editor

Lately when I use the gui editor and try to open a number of guis from different projects, it always opens a gui from a particular project. When I play the game, it shows the correct one. I go back to edit it and it shows me the wrong one. I've closed, opened, moved folders around, etc. Every time this happens, in the console, I see:

Set::getObject index out of range.

I've tried deleting .dso's...