And you have a custom script that, in the custom php page, you define the variable THIS_SCRIPT to be Shop? I thought this was a forum? You can't use THIS_SCRIPT to be unique if it's a forum. You should look at the article on conditions to find a condition if it's a forumid you need.
You also shouldn't leave this line as is:
PHP Code:
$vbulletin->options['shop']='unique_name';
It should have a unique name also (although I guess if you only use the plugin once, it will be unique.)