Streamed transfer + netTcpBinding = framing mode not supported?

Can anybody explain what this error means:

The .Net Framing mode being used is not supported by blah blah yadda

I can't find any info worthwhile. The exception says to check the server logs, however I can't find anything in them relating to this error. I don't know what the hell a "framing mode" is, otherwise I'd try different framing modes.

What I'm trying to do is to create a TCP WCF endpoint to send a Stream to the client.

Here's the interface (prototyping):

[ServiceContract]
public interface IXpsService
{
    [OperationContract]
    Stream GetCurrentDocument();
}