"HTML Form Snippet" generates invalid code....

When you generate the necessary embed code for a profile form that can be used anywhere the form action URL is to the /administrator URL. The action URL should be to the front end otherwise embedding it becomes problematic when you have an invalid form as the resulting page with the errors highlighted ends up in the back end. It is feasible to have all the resources refer to the /administrator URL but not the actual form action URL.

See http://forum.civicrm.org/index.php?topic=23153 for original discussion of error.