RFC in B2B service return NULL

In SAP BC 4.0.1 has a service that calls to RFC in SAP. This RFC updates a table, returns “I” in case of success and “E” in case of error. This service is assigned to B2B Service in Roule Routing.
When the service is executed from the Developer or Integrator, the RFC returns the result of update, but when it is executed automatically by the arrival of a IDoc the RFC returns NULL.