When you update your driver, you have to re-evaluate your system in order to get a new WEI score. Of course, it likely won't change anyway... and if it does it will only be by a very small amount. (From 4.8 to 4.9, for example)
Did it not say "New hardware detected... Your Windows Experience Index needs to be refreshed"?
What do you mean by "it won't work"? Are you saying it doesn't give you a WEI score at all? You have to close system properties after the refresh and re-open it. I would seriously suggest ignoring the the WEI score anyway... it really isn't very useful as a benchmark tool. You might try cleaning the driver out as Gandalf suggests and installing the new one fresh to see if that works.
You are right. WEI score is not necessary. I use Gandalf suggestion, but it did not work. There might be problem in my graphic card. New driver is not suitable in my PC, but the old one. However, i give up and facing no problem with this error.