SAP Idocs not being recognised by the routing rules

I have a curious problem. A job runs each night in our SAP system and genertes approx. 150 LOIPLO idocs. These idocs do not make it into webMethods despite there being a routing rule there to process them. The status of the idocs is 03 which indicated that the idocs was passed to the port OK.

Each morning I regenerate the idocs using SAP transaction WE19.

These regenerated Idocs are picked up by the routing rule and the appropriate service is invoked.

The user id that creates the idocs is a standard user id that creates many different types of idocs and sends them successfully to wM.

Has anybody come across this problem before and what did you do to solve it?