Why the different version numbers for the Norton Security Status

I have 2 laptops. 1 runs Vista Business OS and other runs vista Ultimate OS. Both are protected with NIS 2009 updated to version 16.5.0.135. All other NIS version details are identical apart from the Endpoint ID's.

The Vista Business OS runs NIS gadget (version = Norton Security Status 2009.0) which works fine with UAC running.

The Vista Ultimate System runs NIS gadget (version = Norton Security Status 2009.5) and with UAC running has rotating dots problem. Works OK with UAC off!

Why are the two systems showing different version numbers for the Norton Security Status when both laptops are fully updated?

How can I get the working version (2009.0) back on my Vista Ultimate machine?? Please no reinstall suggestion (I have tried that mmany times and always after restart is faulty with UAC on.