I've been asked to look at an installation (Zen Cart v1.5.1, running on Windows Server 2008 using PHP 5.3.28) where the admin-access is not working.

There's a log generated each time an admin attempts to log in:
Code:
PHP Fatal error:  1062:Duplicate entry '236817' for key 'PRIMARY' :: insert into admin_activity_log (access_date, admin_id, page_accessed, page_parameters, ip_address, gzpost, flagged, attention) values (now(), '0', 'login.php ', 'camefrom=index.php&', '<edited>', '', '0', '')
This is coming from /admin/includes/init_includes/init_admin_history.php, line 57, and it's always that duplicate entry 236817. How could the database get so that an auto-increment field won't increment?

I'm currently waiting to get access credentials for the server to see what I can see. Any ideas would be much appreciated.