I had the same issue, here's how I solved it.
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Run Live Update (Tools->LiveUpdate from BackupExec).
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Close your BackupExec window (and make sure it's not open elsewhere, like another RDP session)
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Start->Run 'services.msc'
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Stop all BackupExec services
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Go back to the LiveUpdate window and continue. It should finish now.
After it's done, check the Event Viewing (Application) to see if you need to restart to apply everything (I did).
If that doesn't solve your problems, you should look in the BackupExec for Windows Servers Installation Log for hints as to why the install failed:
C:\Documents and Settings\All Users\Application Data\Symantec\Backup Exec\Logs\bkupinst.htm (2003)
C:\ProgramData\Symantec\Backup Exec\Logs\bkupinst.htm (2008)