WHMCS login doesn't work


I installed the latest WHMCS WP integration plugin 1.03 but the whmcs login doesn't work.
My php version is 5.2.17.

Error log:
PHP Warning: preg_replace_callback() [function.preg-replace-callback]: Unknown modifier '(' in /home/../public_html/wp-content/plugins/whmcs-wordpresss-integration/whmcs-integration.php on line 551 [27-Mar-2012 09:35:48] PHP Warning: DOMDocument::loadHTML() [domdocument.loadhtml]: Empty string supplied as input in /home/../public_html/wp-content/plugins/whmcs-wordpresss-integration/whmcs-integration.php on line 505

Could you help me please?
Thanks a lot!