Ohio sales/use tax entry

Turbotax won't allow me to enter 0 for the Ohio sales/use tax entry in Part VI of the Information Worksheet.  I'm working on taxes for my son, whose primary residence is in Ohio, but he has been in Alaska in the military, and has not purchased anything in Ohio.  I can't figure out what I did to get this flagged when turbotax did the state review, or how to move forward, unless I enter a value other than 0.