remember Netscape Fasttrack server? remember irix6.4?
That sound you just heard from Seattle was my head exploding. Ouch.
I quickly realized the forum_*.threads files were needed so I 'rebuilt' everything and was good to go. This is the only change on my end that could have possibly caused this problem.
Totally serious here. Go nuke them again, and do another rebuild... and then go back and make sure that they've all been rebuilt.
If it's a problem with the topic data, it should be detected during the rebuild.
If it's a problem with the member data... eh, dunno, this is still a giant set of wtf, and I haven't even looked at the code in over a year, so who knows.