Form 2106, line 47: the amount calculated is 759. I donated my car at a value of $490. T-tax says depreciation allowed is too large, but it is what was calculated. Help!!

My car was old: a 1991 VW Golf. I was only able to get a donation value under $500. But the gain/loss basis calculated was $759. Here's the bad part. When I went back and calculated the depreciation through the 53.5 cent per mile calculation, I ended up with $321 on the depreciation allowed (line 47). The error message that this amount couldn't exceed the basis, but the basis is $490. Last time I looked, 321 is less than 490. What is going on?