Four shadow boxes ruined...

Yep.  For some reason, every tape I am using for masking off the clear spots of the shadow box for the "Zero Dark Thirty" diorama is leaving behind really bad residue.  I've now had FOUR boxes ruined by various problems (one with tiny fractures that I didn't notice on purchase, one exacto accident, two spray paint/tape problems).  I am getting SO damn frustrated.  At this point I think I'll have to use balsa to mask, because every tape (masking, painters, special masking paper) is leaving a residue.  Could the spray paint be causing the problem?

*sigh*  Should have been done a week, and thirty dollars, ago.