To return collection values in ax 2009 custom service

Hi,

How to  return collection values in ax 2009 custom  service.....I tried with Serialization and deserialization example in this below link http://blogs.msdn.com/b/aif/archive/2008/12/16/creating-custom-dynamics-ax-services.aspx but  it showing schema error.. I don't know how to implement a serialization..Any one knows reply to this post..

Thanks & Regards,

Malleswaran