audio_installer.exe problem

So I have tried to repair the game 8 times, I completely deleted and then re-downloaded the game and I still get this error every time...

I looked on the help and it says I'm getting this "because I'm trying to install it on a 32-bit system". Except that I'm not.

I run Vista business 64-bit and every other game works fine (except ghosts of course)

Anyone any ideas??