I do not know the answer, but I didn't want your message to get lost as someone might know.
I think you are saying that twice the value returned was -71 even though not justified by the displayed numbers. If this is the case, my bet is that at some point in pbem play you used uncompressed files; that is, files that were not zipped or rarred. If this is the case, some corruption has crept into you files which returns this false value.
If you concur, the best thing is a fresh install. Just a guess.