Ma Form 1 Section 3

On mass form 1 in section 3 I have a problem with a tax exempt portion as reported on a 1099r.  This pension is from federal employment and is not taxable by the state.  The system says there is something wrong with what I am doing.  I have been doing this for a lot of years the same way.  I went back to my federal income and everything I put in the OPM 1099R entry is correct.  What do I need to do