It depends, but one of the most common reasons is if you have two states listed on the W-2.  Due to MA programming requirements, both incomes get added together on the Massachusetts return.  TurboTax programming can filter this out (there is a checkbox for this), but you then have to mail in the return to Massachusetts.  This is all required by Massachusetts, from the programming to the mail in procedure.  We can't say for certain that that is the reason you can't e-file, but it is a common reason.  Check your e-file rejection code for additional information.