MSMQ Response Delay

I’ve got a VS.Net application that communicates with Navision via MSMQ. I can send messages perfectly fine, and Navision processes these messages very quickly. But when Navision sends confirmation messages back, I find the amount of time to do this can vary widely from 1/10 of a second to as many as 30 seconds! The nature of the message is quite simple - a few text words - so it isn’t that I am doing anything differently between confirmation messages. In fact, the variance can occur when the exact same action is repeated. Any ideas? Waynewil