1- Run command prompt as administrator
2- Type sfc
3- Type scannow

When scanning has finished restart ur computer and install update KB974431

Some computers activations may be reset. activate ur windows again if needed.

I tried it on my 4 laptops

Asus N51Vf
Toshiba A200
HP DV6000
Acer One Netbook

Asus and HP have lost activation, i activated again

All are OK !