“0xe00084f9 - A communications failure has occurred between the Backup Exec job engine and the remote agent” is received when performing a backup of a remote computer.
A debug of the backup returns the following:
 11/02/11 20:04:19 [fsys\shared] - Volume::GetInformation(E:) - Enter
 11/02/11 20:25:09 [ndmp\tpfmt] - Socket error mvrRet = 10060
To allow Backup Exec more time for the target system to perform the processing necessary to respond to the backup commands, try to lower the Remote Agent priority in the backup job properties to the lowest setting. If this does not allow the backup to complete successfully, examine the Windows Event Viewer of the machines involved to look for networking related errors to address, and optimize the networking components in the environment by installing newer firmware and/or drivers or adjusting settings.
Socket error mvrRet = 10060 indicates that a WinSock timeout is occurring.
Winsock errors are TCP/IP errors that occur at the networking layer of the International Organization for Standardization (ISO) model. On both the client and server sides, applications such as Backup Exec, Exchange, Notes, etc. exist above the ISO network layer. The responsibility for establishing and maintaining a reliable network connection belongs to the network and system layers below Backup Exec. If stable TCP/IP connections cannot be maintained, then Backup Exec will be unable to continue the backup once these errors are received.