Thanks much for the response Feline!
First, I just simply add the copyright back manually, so there is no problem there.
About SEF, I have followed the instruction to create a .htaccess file, but after enabling the SEF, I cannot access ANY page of the forum at all.
The URL is changed to "something else" that it keep giving me the "unable to locate" the page error.
I have to disable the SEF for now, but I really like to use this feature.