Backup Exec Remote Agent service on the Media Server has been seen to fail if a VMWare backup jobs end with 'V-79-57344-38264- Unable to copy the virtual machine disk using the VMware VixDiskLib'.
V-79-57344-38264- Unable to copy the virtual machine disk using the VMware VixDiskLib
A hotfix is now available for this issue in the current version(s) of the product(s) mentioned in this article. Refer to the Hotfix link under Related Articles at the end of this article to obtain the hotfix needed to resolve the issue.
Backup Exec 2010 R3 Rev 5204 Hotfix 195395 - http://www.symantec.com/docs/TECH195395