I've tried a little bit of everything! "Schedule C: Auto and truck expenses require evidence to support the deduction. Failure to provide this support on Schedule C Part IV or Form 4562 Part V will cause the e-file return to be rejected by the IRS. If the vehicle in question is a heavy truck, mark the listed property check box or use a method for vehicles over 6000 lbs. in the depreciation input to satisfy the IRS e-file specifications for Reject 183."
I've never heard of an e-file rejection for this, but based on that wording, look at line 47a of Schedule C and line 24a of Form 4562. Is one of those boxes checked as "yes"? If not, I suspect you need to get that box checked.
