I've seen this happen before. Generally when the groups and graemlins table gets duplicated, it means the createtable.php or one of the altertables is still on the server and somebody is running it.
You should be able to remove duplicates with something like PHPMyAdmin and then be sure to remove the createtable.php, altertable*.php scripts and the install.php file. <img src="https://www.ubbcentral.com/boards/images/graemlins/smile.gif" alt="" />
