The ESL "reauthorization codes" change the "last usage date" on the key once. The codes will not work again.

If you're running Version 4.50, download the "hot fix" from November 2006 from this website to avoid this issue (caused by someone running an unpatched version of 4.50). If you're running Version 5.00, download the 070122 build to avoid this issue (caused by someone running an unpatched version of 5.00).