I went to your site, and saw that while I'm a "Guest" the "My Account" link is present in the footer. The reason it gets all squirrely is that the "My Account" page wants to be bound to a customer (and I'm not one as Guest).

Since there's no option for "My Account" in the footer in the standard 1.38a, I'm guessing you've got a custom includes/YOURTEMPLATE/common/tpl_footer.php. Wrap the 'if' statement that niccol suggested around the href for the FILENAME_ACCOUNT link.