Keogh/SEP/Simple worksheet

My husband gets a K-1 from his partnership. They deposit money into a self-employed 401K for his benefit. The partnership doesn't contribute anything, they just do this out of his earnings. The K-1 has code Z and "STMT" on line 20. The supporting statement has his ordinary income (loss), self-employment income (loss), which are the same amount and Health insurance payments listed in the description. I entered the info into TT as directed and when I completed and ran the error check it keeps popping up that I need to put something in the box 6a on the worksheet.  It won't let me enter zero, but the correct amount is already listed in line 6b from his K-1. I don't know what to do to correct the error.

 

Thank you!