The problem is that the program is entering zero for the Prior Depreciation, rather than leaving it blank.
If you are using the CD/downloaded version, you can go into the "Forms" mode (in the upper, right-hand corner). On the left-hand side, look for the "Asset wks", for the the roof. On Line 9 of that worksheet, delete the zero, and it should calculate correctly (it took me a couple of times until it would let me delete the zero).
