The exact same thing happened to me. I'm using v 2.0, but it worked fine and people were uploading/commenting on products. Today I noticed I can't login, no one can. I checked the config-inc.php settings, they're correct.
ReviewPost v2.0, installed since January 06. Connecting to phpBB2 (latest version). Now no one can login. I can't even login to get to the admin panel. I guess I'm going to have to see if I still have a copy of v2 files because I'm sure you guys won't be able to help... It's a few versions behind.
To be honest I don't know when things "broke". It could have happened when I upgraded phpBB
Is there a way that I can upgrade RP without being able to login? I think that's the only way I can fix this.