First, I'm not a fan of running ANY registry cleaner - including ccleaner. They do absolutely no good and can do harm. I'm talking only about using ccleaner to delete the index.dat file, which it does easily. On the main tab (CLEANER - WINDOWS) under "Internet", make sure there is a check mark in the index.dat box and then click on "run cleaner". After a reboot, you can remove that checkmark (you do not want to continually delete that file).