Retirement tax questions

I have an OPM government retirement that is exempt from MA state tax.  I get an error at the end and cannot file. I sends me to a worksheet and wants me to remove my tax exempt amount. But it doesn't reduce down my total income and wants me to pay $1100. More in taxes. How do I get the line above reduced since I can't edit it? Why isn't the software corrected to be able to correct where this pension reflects it is non taxable?