I'm using vB4.2.0 and there's no hook on line 204 of functions_login.php but you probably have a plugin for either "login_verify_failure_username" or "login_verify_success". Find the plugin that uses one of these and on line 4 of the plugin change
split(.........)
to
preg_split (..........).
See
http://php.net/manual/en/function.split.php and
http://www.php.net/manual/en/function.preg-split.php