Form SD-100 is an Ohio local tax form.

• On your W-2, be sure both boxes 16 and 18 are posted.
  • Box 16 - Sate Income
  • Box 18 - Local income
• You should also run the State Review
  • This can be found under the state tab on the left sidebar.

There are two types of School District (SD) Income Tax (SDIT) in Ohio, Traditional and Earned Income.  Traditional taxes the  Ohio AGI from your state tax form (line 3). Earned Income taxes box 18 of your W-2.  If you have self employment income, instead of a W-2, it gets a little messier. 

I'm having the same problem. No matter what number I put in that box it gives me an error. Could someone please explain in plain, everyday English exactly what I'm supposed to put in the AGI box for SD 100?

Read everything on that page. TurboTax usually tells you  a suggested amount.

Not helpful 

What is the message on the screen?   Is the error regarding the dates of residency or something else.   You should exit the review and go back to your OH tax return and review the school district entries there.   @Jesavaille 

Problem resolved. I had to re-enter the value for modified gross income that was on the form