error starting web service dispatch

We're on version 3.0.3.7171. I've been using Mirth for many years, but am new to using web service / SOAP sender channels. We have a channel set up that receives lab orders via TCP Listener, and sends them via Web Service Sender. But we're getting the following error:



Web Service Sender error

ERROR MESSAGE: Error creating web service dispatch

java.lang.NullPointerException



I imagine you'd need more info, but...what kind of things could cause this type of error? Supposedly, this same channel works for other clients... Thanks

error starting web service dispatch