Content deployment fails - the request failed with an empty response

Hi, I'm trying to run a content deployment job but it is failing with the following error. I can't determine from ULS logs what is causing this. 

System.Web.Services.Protocols.SoapException: the request failed with an empty response. 

I can browse fine from my staging part to the production CA server and can set up the path without any problems but it all goes wrong when I actually kick the job off. 

Can anyone shed any light on possible causes? I thought it may be a port issue but the 80, 443, 445, 32843-32845 ports are open and a firewall sniff doesn't pick up any denials.

Any help appreciated. Thanks