Hmm, nope, 3dROIMaker shouldn't care whether it was a Z-score, a T-stat or any other data sets-- it's all just numbers.
One thing to check *might* be if there were NAN or bad values somehow in the T-map that aren't in the Z-score set.
However, the skeletoning part certainly shouldn't cause badness, either, so I'd like to see what's going on there. I don't know if you can attach the data sets (Z, T and FA) with a PM, otherwise I just sent my email address in a reply PM (not that it's secret, but I've never had a case for using the PM function before).
--pt