NooB here...
I'm have an unusual situation. I just made the Jump from phpBB to Xoops. I'm finding out the same members on my Old site that I had to manually enter their Registration. Are experiancing the same problem with XOOPS CMS as they did with php-Nuke. Are they being filtered out? This isn't a Global problem with Registration, Members are Signing In with no problems. It's just a few are getting the "Not Accepting Registration" Could this be a ISP problem on their side? Thanks for your Help in Advance.- bob

Running the latest release of Xoops
Old Site... phpNuke ver, 7.6

Do you/they have Norton Internet Security? Personal Firewall can prevent registrations on XOOPS based sites.

You might want to try customizing the Personal Firewall, or disable it all together when signing up. You will also have to disable it when accessing the Administration Control Panel.

If you don’t want to go a moment unprotected, you can always operate with 2 firewalls, using something like Zone Alarm (free) as the backup firewall when you have to disable Norton Internet Security’s Personal Firewall for any reason.

Hope this helps.

Thank you for your recommendations, I'll pass this along to my Troubled Members...
I'll add a small Note on my Top Page about the Items you listed. I'll report back ASAP!