for MS State resident return: 

 The following diagnostic is generating:  e-file: When a Credit for Income Tax Paid to Another State is present on Form 80-105, line 18, Mississippi requires a copy of the other state return to be attached as a PDF for electronic filing (ref. #32480)

I have to admit, this is the most interesting post so far this week.  As a side note, did you attach a pdf of the other state return to the Mississippi return?