At offset A2 in ATADDBN, it has just stored a valued into itself. So this module is not truly reentrant.
It must be defined in sysgen as NOPROTECT
Here is the PROGRAM definition as it should be defined to your system:
ADD PROGRAM ATADDBN CONCURRENT DYNAMIC DUMP THRESHOLD IS 0 ENABLED ERROR THRESHOLD IS 5 ISA SIZE IS 0 LANGUAGE IS ASSEMBLER MPMODE IS SYSTEM NOMAINLINE MULTIPLE ENCLAVE IS ON NEW COPY IS ENABLED OVERLAYABLE PROGRAM NOPROTECT REENTRANT NONRESIDENT REUSABLE SAVEAREA.