DSNE110E `ssid` NOT VALID SUBSYSTEM ID, COMMAND TERMINATED

Explanation
  There is no subsystem id with the name identified
in the message as 'ssid'. The subsystem identifier you specify (or
default to) on the DSN command must exist. This message is the result
of specifying (or defaulting to) a nonexistent subsystem identifier. 

System action
  The DSN processor ends, and control returns
to TSO.

User response
  Reissue the command with a valid SYSTEM parameter.