Backups, backups, backups.

One time, I spent 10 hours trying to fix a layout like this.  There are too many variables that could be causing the crash to really give you much of an idea.  Most often for me it's an incorrect file reference... somewhere.

Best way to troubleshoot it is to save-as with a different file name, then go through the text document and see if you can't remove a category of elements in the layout.  Personally, I split everything up into folders like 1) Tiles, 2) Monsters, 3) Treasure, etc.  So, I'd go in and remove all the tiles, then try to load the layout in GUTS.  If it doesn't open, replace the deleted category and repeat by deleting a different category.  Continue until it works and you'll know which folder the faulty piece is in.  Then carry on with the same process as you work your way deeper into the folder.