Usa FB.ui() como te comenté, creo que es la solución correcta y duradera.
Y por favor, comunícales a tus clientes que FBML es considerado como obsoleto por el mismo Facebook y en muy poco tiempo será completamente deshabilitado.
Cita:
Iniciado por http://developers.facebook.com/docs/reference/fbml/ We are in the process of deprecating FBML. If you are building a new application on Facebook.com, please implement your application using HTML, JavaScript and CSS. You can use our JavaScript SDK and Social Plugins to embedded many of the same social features available in FBML. While there is still functionality that we have not ported over yet, we are no longer adding new features to FBML.