Here's the answer, from turboTax support. The error is showing up in FORMS MODE on the Sec 179 Limit form not on the Form 4562. If you click on Form 4562 on the left you will see that LINE 10 is not populated with the prior year carryover number. Populate line 10 and line 12 with your total carryover. Once you populate these lines the error on the Sec 179 Limit page will go away.
