error says, "Target agent servername is unavailable"
It means, the Agent is not running/accessible.
In staging phase, appserver copies the packages to target system.
But in this case the target is not accessible, so the appserver can't copy the relevant packages.
that's why, the job fails.
Is you can browse the target Server? (try agentinfo on target from NSH prompt.)
Is the Job Cancelled by User or AppServer?
if possible, attach log files.
Target servers are alive, and accessible from appservers. Jobs weren't cancelled by any user, so believe it should be because of appservers.
All the servers have passed the simulate phase, and also some of the files have been copied from patch repository to the target servers during staging (so, there shouldn't be any issue with agent connectivity), and the job failed in the middle of the staging phase with the subject error.
Also, i don't see any relevant error log in the appserver log, and the targets rscd.log about this issue during the time stamp when this error occurred.
My default Job time out is set to 90 mins, and job part time out is 15 mins.
This issue has been resolved after the increasing the Job Part Time Out value to 30 minutes as the patch deploy job was trying to copy the payload data (huge file size) to the targets servers, and it took longer time than the earlier timeout value of 15 mins, and hence the appserver cancelled the timed out work item thread, and hence the associated Job.