You can use the following technote on Symantec: http://seer.entsupport.symantec.com/docs/305549.htm
What i want to mention here is, if you’re somehow failing to backup your sharepoint objects/portals, you can try the following:
Change “Backup selection” in your backup policy to:
Microsoft SharePoint Resources:Windows SharePoint Services Web Application*
And try again with this setup.
It worked for me…
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Addition:
I had problems finishing a backup which actually started successfully.
It was failing after some amount of time and/or data.
Try the same backup with every firewall/ips bypassed between the media server and sharepoint server.
Firewalls and ips’ can sometimes cause trouble after some time, although the backups could start without problems.