SAP Message XS815 - No delivery, as reference & cannot be resolved

Diagnosis
The message could not be sent to a recipient as reference &V1& of thenode could not be resolved.

System Response
Processing was ended.
Additional information of the node used (in the system langauge of thenode):
V4

Procedure
Make sure that the node has access to reference &V1& type &V2& or amendCustomizing for the node (ability to resolve references).