Error 404 when trying to log in,
 

When I try to log into my forums I am directed to an Error 404 page. What would cause this, and how can I correct it?

Also, when I try to go to my admin cp (www.mysite.org/forums/admincp) I get this error message:

Warning: array_merge() [function.array-merge]: Argument #1 is not an array in [path]/includes/init.php5 on line 275




Unable to add cookies, header already sent.
File: /homepages/16/d205872612/htdocs/theparentpack/forums/includes/class_core.php5
Line: 3277