You could not claim QST on union dues if you do not have the QST id form the employer. This is probably the error that you got. to fi it go back under "Deductions" and "Union or professional Dues" and unselect YES to this question, If this is selected to NO, you won't get the error in the review process.
Did you pay GST, HST, QST and are you entitled to theGST or HST/QST rebate ?