On the mainframe, there are two frequent causes of operational errors:
The CICS or SNA operator varied the resource out of service.
SNA placed the line, physical unit (PU), or LU into a non-operating (INOP) state because of a network outage.
In these cases, either:
The DirectConnect for z/OS Option Administrator receives SNA software time-out and connection failure messages in trying to start up DirectConnect for z/OS Option, or
The requesting client receives an SNA software message indicating that the system could not start the RPC.
When you are contacted about such messages, reactivate the necessary mainframe resources.