The segment you are showing me is missing an Entity Type Identifier after the NM1*.
Usually this is two characters (i.e. IL means subscriber, QC means patient). For most specifications this is not a problem, but since the 837 identifies multiple loops that start with NM1, it uses the Entity Type Identifier to resolve the Name loop
that it is attempting to parse.
Have other systems you work with been able to parse this X12?
Do you know which Loop this should be representing?
I could modify the spec so that this won't cause an error, but it would basically be an unidentifed loop.