JAX-RS bug after upgrading Jackson to 2.2

[Nic Fellows]

I have just upgraded from Jackson 2.1.1 to 2.2.2 and it has caused the 
following exception:

 javax.ws.rs.client.ClientException: .No message body writer has been 
found for class : class uk.co.tbp.gabble.domain.User, ContentType : 
application/json.

Has something changed in the way I need to configure the provider?

Nic