If I enter dividend data on line 1a and then again on line 1b, the program fails to calculate tax. Is there a reason for this?
Many parts of the 2017 program are not fully operational yet and will not be until sometime in January or February ... now are you sure the QDCGT worksheet is not working correctly ? Did you enter in all your income yet ? Switch to the FORMS mode and look for that worksheet. If your income is low enough then you will possibly pay zero tax and that would be correct.