You have to use the [Unsubscribe] tag. What is your MLM URL?

The correct URL is http://www.martialartsbusiness.com/lm/lm.php however if you go there with your browser you will get an 'Internal Server Error'. It is very likely because of a permissions problem with the 'lm' folder on your server. Try to set it to 777, 775, 755 or 705.

Depending on your server it has to be 777, 775, 755 or 705. You have to try until you get it to work. Only apply the permissions to the folder, not the enclosed items. Your unsubscribe URL is wrong because you MLM URL in your preferences is also wrong.

All that is explained in the MLM documentation and FAQ.

From the FAQ, entry #4:

When I run a MLM command with my browser I get an 'Internal Server Error'.
That means your server doesn't like you to set the folder 'lm' access permissions to 777. Just CHMOD the 'lm' folder to 775 and try again. If it still fail CHMOD the 'lm' folder to 755. If it still fail CHMOD the 'lm' folder to 705. It should then work. You can CHMOD a folder with your FTP software.