It looks like you have a url problem. The link you posted was to this:

http://www.uooutpost.org/httpdocs/ubbthreads/adduser.php

when actually, it is this:

http://www.uooutpost.org/ubbthreads/ubbthreads.php

I think you need to remove that httpdocs portion from your $config[phpurl] variable in your config.inc.php file for it to work properly.

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Rick Baker
UBBThreads developer