The Dimensions server initially tries to log in to a remote node using the same credentials as the server account. If you have a MVS RACF account called DMSYS with the same password as the Dimensions account DMSYS, the server will log in as this user. You can switch this behavior off. For information, see the description of the following variables in the Dimensions for z/OS User's and Administrator's Guide:
DM_MVS_REJECT_USERS (in the MVS configuration file).
DM_SKIP_SERVER_CRED_CHECK (in the server configuration file).