For ADAM system programming, where no assumptions may be made about the working order of either the ADAM parameter or data systems, another subroutine library, EMS (the Error Message Service) is available. The subroutine calling sequences for EMS are very similar to those of the Message and Error Systems (indeed many MSG and ERR routines are implemented as straight-through calls to EMS - hence the occurrence of EMS error messages from MSG or ERR routines).
The Error Message Service library is intended specifically for use in ADAM system or general low level subroutine libraries. It should not be used in applications software.
MERS (MSG and ERR) Message and Error Reporting Systems