app icons missing

I've changed my icons in some of my apps. Some changed successfully; the changed icons can be seen in the launchpad and dock. However, the system preferences has no icon in the dock, as well as the google chrome, iTunes and system preferences again in the launchpad. Ugh. Don't know what to do. Btw, Mac Lion 10.7.4

How did you change them? Did you replace the actual icon file inside the app, or drag an icon file onto the image in the "Get Info" window for the apps?

I just found out that CandyBar, an icon organizer for OS X, is now free. It can replace system icons and individual app icons with ease. They don't officially support it anymore and the future is uncertain, but I can attest that it works very well. Just don't do anything rash like delete the backups it makes.
Panic Blog » CandyBar, Mountain Lion, and Beyond

I changed it by copying and pasting the icon in the Get Info... And do you know why there are some icons that do not have their "supposedly" icons? I mean, the icon in its get info is not the same icon. Sometimes, it would be the icon of png or jpg...