You may have some member in there that you changed the registration date on. I believe I have this assuming your member files are in the same order that they registered, so if one was modified it might screw it up. Not for sure on that though as I don't use UBB anymore. I've moved to the "other" board.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.
