Well, if it only affects some members, and the web server gives you that error, it's some sort of security apparatus on the server, likely mod_security; the error logs on the server and/or the mod_security logs will list WHY this particular user is locked (likely it's some word randomly used in their profile).

BTW, I be James tongue

I am a Web Development Contractor, I do not work for UBBCentral. I have provided free User to User Support since the beginning of these support forums.
Do you need Forum Install or Upgrade Services?
Forums: A Gardeners Forum, Scouters World
UBB.threads: UBBWiki, UBB Styles, UBB.Sitemaps
Longtime Supporter & Resident Post-A-Holic
VNC Web Services: Code Modifications, Upgrades, Styling, Coding Services, Disaster Recovery, and more!