google analytics form on the frontend

Using the Multisite Analytics plugin, I am trying to put a form on the frontend that will allow MarketPress store owners to track their sites.
I've put the following code in my template file

<div class="GoogleAnalytics">
  <h3><?php _e( 'Tracking Settings', 'basic' ) ?></h3>
  <form method="post" action="">
    <table class="form-table table table-bordered">
      <tr>
        <td>
          <input type="text" name="tracking_code" class="regular-text" value="<?php if ( !empty( $site_settings['track_settings']['tracking_code'] ) ) { echo $site_settings['track_settings']['tracking_code']; } ?>" />
          <span class="description"><?php _e( 'Your Google Analytics tracking code. Ex: UA-XXXXX-X. The Site tracking code will track this site.', 'basic' ); ?></span>
        </td>
        <td>
          <p class="submit">
            <?php wp_nonce_field('submit_settings'); ?>
            <input type="hidden" name="key" value="track_settings" />
            <input type="submit" name="submit" class="button-primary btn btn-success btn-mini" value="<?php _e( 'Save Changes', 'basic' ); ?>" />
          </p>
        </td>
      </tr>
    </table>
  </form>
</div>

The problem I have now:
When the user presses the "Save Changes" button, he is redirected to this url:
options-general.php?page=google-analytics&dmsg=Changes+were+saved%21# which (of course) doesn't exist.
On top of that, when re-accessing the form, it is empty. The tracking code field has not been saved and is empty.

Does anyone have any tips on how to address this?