That is the exact situation I was in - a loss on line 4c and the system would not accept 0 or a negative number. I ended blanking out the field for line 18 and ignoring the error. (None of the work-arounds worked for me - I tried them all.) When I submitted my return, the schedule SE for the business in question was not included. Make sure you have fixed all other issues, but it seems safe to ignore this one if your business had a loss and no Self Employment taxes are due. Hopefully TurboTax will fix it before too much more time goes by. Good luck!
