I also had this Error:
Code:
Warnung: preg_replace() [function.preg-replace]: Unknown modifier '2' in [path]/includes/class_postbit.php(321) : eval()'d code (Zeile 113)
But i think it could be the Problem with parsed URLs or a Language Problem. I have a German Forum and i try to retrieve Titles from URLs with vbSEO. I removed my wrong Link and it worked again on that same Page.
So maybe if there is no English Language or ASCII Code, your Hack gets confused...
In my Case, this was the Problem.