Login form - hook_form_alter destinations broken
I think in D7 you can also use the redirect property, this would be in your form_alter:

  $form_state['redirect'] = array('http://www.example.com/my-external-path', array('external' =&gt; TRUE));


$form_state['redirect'] takes the same values as drupal_goto(), which itself uses url() to generate its destination path. It is possible to add an array of options including 'external=TRUE' to your redirect value if redirect is external.

Not sure if this will help in your case though.