Quote Originally Posted by gossamerLL View Post
Zen Cart 1.5.1
Recently upgraded from 1.3.9

PHP Fatal error: 1146: Table 'databasename.Table_ANTI_ROBOT REGISTRATION' doesn't exist :: DELETE FROM TABLE_ANTI_ROBOT_REGISTRATION WHERE timestamp < '1384979001' or session_id = 'a really long number' in ....catalog/includes/classes/db/mysql/query_factory.php on line 120

Results in an error on the login page and users can't create an account.

What should I try?
It looks like you are missing a definition file. Log in to your admin and see if you can find the missing variable. The missing variable is the one that begins with table_ If you find a define for that variable then I am wrong. If you do not find a define for that variable then you will need to up load the applicable file that has that variable for that plugin.