When the standalone installer is used on a Windows 2000 or 2003 server with Terminal Services, installation can fail with the error dialog 'Installation failed'. The installation rolls back, but subsequent attempts at installation fail. An error message is generated:
Error 3000.An older version of Sophos Anti-Virus has not yet been fully removed from your machine......"
This has been experienced on both Windows 2000 and Windows 2003 servers running Terminal Services. This could happen where the installer was launched from a path to a remote folder (network share). Terminal Services caused the installer to execute some operations with insufficient rights to access the remote folder.