Smart Check Error Indicated but not possible to correct

I'm in the "Review" tab and when I run Smart Check it says I have 1 error. Here's the message:

"Tax Summary: Itemref is marked as estimated. Enter the correct number, then select "Unmark Estimated" from the Edit Menu.."

The form shown is the Tax Summary. I checked every number on the form and there's not one that is marked as estimated. When I continue and run Smart Check again I get the same error. 

Is this a known issue and how do I resolve it?