Suggest changing code in bm-custom-login.php from:
$pluginUrl = get_option ('siteurl') . $pluginPath . plugin_basename (dirname (__FILE__)) . '/bm-custom-login.css';
to:
$pluginUrl = site_url() . $pluginPath . plugin_basename (dirname (__FILE__)) . '/bm-custom-login.css';
to help eliminate errors like "You have requested an encrypted page that contains some unencrypted information. ..." if you are using SSL to encrypt login and administration.