I have a transactional queue called myPrivateTransactionalQueue hosted on a Win2008R2 server called myReceivingServer which should receive messages from another server calle
Check the sender dead letter queue for a clue.
On my case, after checking the sender dead letter queue I was able to identify that it was a permissions issue.
When the queue is unauthenticated it is not enough to give permissions to "everyone" but "anonymouns logon" must also be there with at least send permissions.
Ok I had exactly the same problem and it either resolved itself because of two reasons. I updated the computer name referenced in the message I was sending (previously it was an alias in my hosts) or it could have just been the fact that I enabled full control to everyone/anonymous on the receiving server and rebooted the machine.