I'm having the same problem, and my permissions and directory settings all check out.

Looks like installation isn't the only time this happens. I gather from the following posts that it may be an issue of varying perl installations?

FYI, see these posts in the "UBB6 Bugs" forum:

Topic: UBB 6.0 cannot create new member files http://www.scriptkeeper.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=28&t=000103

Topic: New reg users problem? http://www.scriptkeeper.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=28&t=000096


And this thread in the "UBB6 Post Installation Troubleshooting" forum:

Topic: New Registration / Blank Screen http://www.scriptkeeper.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=31&t=000008


Looking forward to hearing about the fix. Thanks!
josh