I just tried to register on your site(Successful) But to change preferences or profile I get the same error. In looking at the url on the page it seems to be missing part of the string at the end(ubbthreads.php?ubb=editbasic&u=1) the "&u=1" part is missing.
I still think it is some type of path problem and you need to contact UBB to open a ticket. Or you have a corrupted file somewhere.
You have had way to many problems for this upgrade and it is time to call them.
