VMware policy backups failed with error : "10 allocation failed" during a particular period.

[Rocky67]

VMware policy backups failed with error : "10 allocation failed" during a particular period.
When retriggered later completed successfully. The issue re occurred again after 2 days. I checked the master and media server, Backup host and they have enough memory. Also, did not find any error in messages directory of master(sunos master). Did not find any in events in media server, Backup host(Windows). What could be the possible reason.

Checked the failed jobs and could find there are many ESX hosts for which the VM backup has failed and not just 1 ESX host.

NetBackup version is 8.1.1

[Marianne]

Which SunOS/Solaris version on the master?  

Have you tried to monitor memory and cpu usage on the master during the period when issues are seen? (This can be configured by server owner using cron).
The issue could also be with shared memory and not really with physical memory. There are TNs about this (some for media manager processes, but still worth a look).

You will only know the real reason if you can have a look at everything happening on the master during that period.