Problem on the comment form #validation and #submit
You're missing $form_id, the third parameter of the function. 

See hook_form_alter() reference on drupal.org. The problem you're experiencing might be a (weird) way of PHP reacting to that. 

In situations like this you may want to check for errors on the logs (Drupal, PHP, MySQL). Some times there are useful hints there to figure what's wrong.