Client s/w kits always have to be installed before any agent kit(s):
1) Install "base" GA (General Availability) plain client kit.
2) Install "base" GA (General Availability) agent kit.
3) Install client MP kit (e.g. current highest is MP7 for v5.0, or MP6 for v5.1, or MP4 for v6.0).
4) Install agent MP kit (e.g. current highest is MP7 for v5.0, or MP6 for v5.1, or MP4 for v6.0).
Base "GA" kits are on CDs, and cannot be downloaded (except via vLicence site).
All MPn kits are always available here:
...here for a full list of all tech notes and downloads for NBU ES by date:
...or the same thing, if you know exactly what you need for NBU ES (in filename order):
HTH,
Regards,
Dave.