You may need to walk through the interview for this section in order to fix this.  Try this:

1. Log in to TurboTax and click Take me to my Return
   
2. Type in Schedule C in the Search box and click on Jump to Schedule C
   
3. This will bring up your Schedule C business. Click Edit next to the business you are getting the error for.
4. Click continue until you reach expenses.  Check your entries there. 
   
5. Then hit continue until you reach the end of the section and continue to Run the Federal Review again. 

If this form was created in error and the above doesn't solve it, try deleting the Form. 

To do this go to (left-hand side of the screen in the black bar)

Tax Tools> Tools> under Other helpful links..choose>.Delete A form