ABAP Dump while creating return purchase order

Hi,

I am facing an issue in creating return purchase order. After selecting order type as "NB2" in ME21N transaction, the system throws below dump

Category               ABAP Programming Error
Runtime Errors         OBJECTS_OBJREF_NOT_ASSIGNED_NO
Except.                CX_SY_REF_IS_INITIAL
ABAP Program           SAPLMSR_MEPO
Application Component  LO-ARM
Date and Time          26.06.2015 10:19:40

     An exception has occurred which is explained in more detail below. The
     exception is assigned to class 'CX_SY_REF_IS_INITIAL' and was not caught in
      procedure
     "MSR_PROCESS_PO_PROCESS_HEADER" "(FUNCTION)", nor was it propagated by a
      RAISING clause.
     Since the caller of the procedure could not have anticipated this
     exception, the current program was terminated.
     The reason for the exception is:
     You are trying to access a component with a 'ZERO' object reference
     (points to 'nothing').
     An object reference must point to an object (an instance of a class)
     before it can be used to access a component. The reference has either
     never been set, or it was set to 'ZERO' with a CLEAR statement.

I have done the necessary configuration for this order type.

How to resolve this?