If your thread is an outbound thread, on your Inbound tab under Thread Configuration, check to see if the Trx id determination Format is set to HL7. If so, and you have a version set on there, the route id HAS to be there or you will get your error. If you are using a variant, just add ACK^RDE as a valid message type. You should be able to use ACK^A01, etc. as an example on how the message is constructed.
