Vista wants me to activate it again,even though its already activated

I installed vista on my macbook pro under bootcamp a few months ago. i activated windows. now, since installing parallels, i have been using the previously installed version of vista, but all of a sudden its asking me to activate windows, so when i do it says my key is already in use, and if i should have another key. why is this, and what has gone wrong?
As im using the same installation of vista that i use via bootcamp, does vista see it as two different installations or something?

 

Vista detects a hardware change since the hardware under Parallels and under Bootcamp are not exactly the same. Vista is very hardware sensitive. I put a faster processor in my PC and had to go through the activation via telephone process. Follow the process given on the screen to activate via telephone.

 

went through the phone process you mentioned. works fine again. very annoying though. had to type in a 48 digit numeric code!!!!