Upgrade prompt at each startup- doesn't complete

Hi everyone,
I have 4.0.3844 (may 5,2009) installed and there's a new update (4.0.3.845) that prompts each time I boot up. So I run it and it goes through a couple steps and then goes blank. It's not going through. It says Conflicting Virtual Machines; what do I do?

I am running Vista on Mac 10.6.1

Thanks in advance

Robin