You don't have to have a business to have a NOL. It can also come from moving expenses or theft and casualty losses.
The error implies that there is an explanation statement for a NOL carryforward attached to your tax return. How it got there is probably not relevant unless you really did have a NOL carryforward from the prior year; check the TurboTax's Carryover Worksheet.
You can remove the explanation statement by either revisiting Business Deductions and Credits -> Net Operating Loss and confirming deletion of the statement or you can delete the explanation statement in forms mode of the CD/Download version of TurboTax or in the Tools section of the online version.
