1Password seems to uninstall itself

This is an odd one. I got prompted to update 1P on Windows 7 Professional. I updated the application and was able to open it.

I then did some M$ and anti-virus updates and restarted the computer. When I did, 1Password was gone.

Now, when I run the "1Password-1.0.9.333" installer, I can see it installing all the files into the appropriate folder (program files/1password)...about 17 files in total....but just near the end of the installation process, a number of files suddenly disappear...including the 1password exe file...and so I can't run anything.

Being mostly a Mac user (Windows 7 is running under bootcamp) what is it that is causing this?

Cheers,

Phil