"The token provider cannot get tokens" (System.ServiceModel)

Trying to sign my WCF messages before they go of to a messagequeue
(using 'netMsmqBinding') to allow the retriever (the WCF service) to perform
impersonation, I am constantly presented with the exception seen in the
subject.

The errortext is: "The NetworkCredentials provided were unable to create a
Kerberos credential, see inner execption for details"
Inner Exception: "InitializeSecurityContent failed. Ensure the service
principal name is correct".

As I'm using MSMQ as intermediate, I do not communicate directly with the
final WCF service, I communicate with the msmq (public queue). Is the queue
the one I should put as SPN in the Client's app.config?
And if so - what format does a SPN for a msmq require?

If this is unclear, please let me explain in further detail.

/Claus Konrad