Go into your XOOPS directory and edit the file mainfile.php.
Change the line where it says
http://yoursite.com
into:
http://www.yoursite.com
Tadaaaaa
That's it. As I understand in a vague way a double login occurs. First from the www.name.com address, then when you press a button the request comes from the name.com system which confuses the russian which is sitting in the cpu and is responsible for access security.He sends you back to the gate to get a new pass.
Cheers and let me know if it woiked!
Rainer