Thanks Chuck. I actually just figured it out. I recently upgraded
VB and when I did I used a different database name (so I could get my test forum up and running before making the live switch)
I forgot to change the database name in Photopost, so it was looking at the old database. Anyone who had changed their password or signed up new since the forum upgrade would be having problems logging in. But most of my members were fine because their old passwords were still in the old database.
Anyway, updated my database name in PP and all is solved.
Thanks again!