MMF2 Not working

I just downloaded the MMF2 Demo (Im on holiday and my disc is at home) a couple days ago and after using it for 2 or 3 days it now says its not compatible with the version of windows Im running. Has this ever happened before to anyone? If so, how do I fix it?

EDIT: Im on a 64bit WIndows Vista Home Premium, Gateway Notebook with 4GB RAM and 200GB HD

Ill try to re-download it......

It worked! Thanks Little voice at the back of my head......