In the last few weeks my site has had two instances of the central scheduling
mechanism failing without evident cause. We have an MVS server at 3.1.2.1.
Both of the clients involved were at 3.1.0.6. One was an AIX system and the
other was an HP-UX 10.20 system. Both use TCP/IP communications. Both have
'schedmode prompted' in the dsm.sys file. A 'query status' command reports
that the server supports any scheduling mode. In each case the server log
showed a message reported that a client event had missed its start-up window.
When I checked the client the 'dsmc sched' process was still running in each
case. When I checked the dsmsched.log file I found the following at the end of
the file in each case:

Messages reporting execution of the last successful event
Messages showing the results of querying the server for the next scheduled
event
A message reporting that the scheduler process was waiting to be contacted by
the server

All of the messages mentioned above had time stamps within a few seconds of
each other. In each case I stopped and restarted the scheduler process and
subsequent events were carried out on schedule. In the HP-UX case, I checked
the dotted decimal addresses used for client sessions before and after the
failed event. They were the same. In the HP-UX case, I updated the schedule,
creating a sequence of events like the following:

Successful event
Query for next event
Schedule change
Event created by schedule change (which failed)
Event reported in response to the query

I don't remember whether the AIX case involved a similar schedule change.

Does anyone recognize this as a known problem? Failing that, does anyone have
any suggestions for tracking down the cause?