January 7th, 2014, ROMVault 2.1.20
HAPPY NEW YEAR.
And after much searching and trouble I believe I have finally tracked down ´comparing null ulong?´ error.
You had to have:
a) a missing CHD file that did not give a SIZE in the CHD DAT
b) a missing ROM file that was zero length and so no CRC supplied in the DAT
c) have a fix for the CHD
d) have the order of things so that the CHD would be fixed before the ZERO length file.

And then you got the ulong? error message.
Anyway finally tracked that one down, and put the correct checks in place to handle missing Size/CRC information better.
So go grab 2.1.20, and keep on fixing.