Microsoft has changed the backup tool in Windows Server 2008. You can not use old Windows Backup Tool (NTBackup.exe) to take backup. You need to use Windows New backup tool to backup anything on Windows Server 2008 computers and also you can not restore the previous backups created by NTBackup.exe on Windows Server 2008.
Microsoft developers have designed a new version of NTBackup to restore the previous backups created by NTBackup.exe running on previous versions of Windows.
You can download the tool at the below URL:
Utility for restoring backups made on Windows XP and Windows Server 2003 to computers running Windows Vista and Microsoft Windows Server 2008.