OS X :: Leopard Dock/Can't Right Click Or Remove Items

I don't know what happened but for some reason, I can no longer right click or remove any items from my Dock

I have Onyx installed which has an option to lock the dock, however that is off. I am certain that my dock isn't locked because I am able to move items around the dock, and also add new items

I don't know when this started but it may have been because I was changing the dock's appearance by replacing some of the pictures in the system files (frontline.png, separator.png etc.)

I've restarted my Macbook a couple of times and have also done killall Dock in the terminal but everytime, I still have these two problems

Also, when booting up my Macbook now, the dock takes much longer to load. Before, it would usually be one of the quicker things to bootup but now it is always the last (before Quicksilver was usually the last program to load for me)

I also used a Terminal command to add a "Recent Applications" stack by following instructions posted here:
[URL]

I've since removed this Stack but the problem still occurs. Don't know whether or not this had an impact or not