Sorry, I don't have the code for the other package - it's installed on a system to which I don't have direct access, and the sysadmin has, as yet, not responded to my request for access to the code.
I can tell you, though, that it's UBBThreads, from Infopop.
As far as I can tell, the authenticate() function queries cookies from the user's browser and uses those to establish whether or not the user is logged in, what forums have been visited etc. During this function it queries the database, which is where I see the failure.
Sorry I'm not able to give more information - I guess I was just hoping someone would recognise the symptom and say "oh, yes - change x to y"