Icon won't stay changed

I've created an icon to replace the awful Yahoo! Messenger icon and replaced it in the Get Info window. I changed it in the application folder and then drug the newly changed icon to the dock where it showed up with it's new icon just as it's supposed to. However, when I click to open the application it reverts back to the original icon. It also still shows the original when I'm tabbing between applications. Can't figure out what else to do. I've restarted the application, I've even restarted my whole machine... nothing changes. I've done this plenty of times in the past and have never seen this before. Any suggestions?

Thanks