Preg_Match Error in Header
 

Got my forum back online and now i'm getting these errors with my stock functions.php and class_core.php files.

In my header it shows:
Warning: preg_match() [function.preg-match]: Compilation failed: regular expression is too large at offset 655370 in [path]/includes/functions.php on line 824

and when I try to go to a link it shows:
Unable to add cookies, header already sent.
File: /home/content/g/r/o/groupfive/html/forums/includes/class_core.php
Line: 3277

Both of the uploaded files are stock, any ideas?