What version of osTicket are you running? Please ensure that /include/client/footer.inc.php actually exists.Have you modified your installation? I ask because common_footer.inc is not an osTicket file, and I cannot find any reference to that anywhere in the current version (1.8.0.2).You haven't really given us enough information to actually help you.
Please help us to help you by reading and following the posting
guidelines located in this thread: Please read before requesting assistance. Thank you.