How do I validate a form field in Codeigniter when using Get parameters?

I have a form that worked perfectly until I switched the form to method="get". Now I can't get form_validation->run() to evaluate to TRUE.

This is how I open the form:

echo form_open( '', array( 'method' => 'get' ) );

This is the only piece that needs to validate:

$this->form_validation->set_rules( 'states', 'states', 'required' );

This is how I check to see if the form is validated:

if( $this->form_validation->run() == FALSE )

Is there something else I need to do to use Get parameters? I have get parameters turned on in the config ( $config['allow_get_array'] = TRUE; ). The form works ok if I skip the validation, so I know the CI system is reading the url fine.