In the last couple hours, I deleted the full version of the UBB and I re-installed the demo. I got it working.
So (don't laugh too hard) I deleted the demo board and installed the full version yet again.. and no go.
Does it matter which of the two versions I downloaded from the members section? One lists /bin/perl and one lists /usr/bin/perl or something like that... Then again, I'm pretty sure this part does not matter under Windows NT.