The best way to combat this is to force user image sizes (specify 64 by 64). Clear your cache and that'll temporarily fix your problem. To manually fix it, go into that person's profile and clear the picture field.
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.