Default folder icon problem

I recently changed the default folder icon on my MBP. I restarted my computer today for, I think, the first time since changing the default. The generic folder icon has changed to a blank page with the top right hand corner turned, and the usual method of changing this hasn't worked for me; I am unable to paste a new icns image. I'd appreciate any advice or solutions, thanks.

Thanks for the link GGJ, but I'm afraid it's not much use to me at the moment. My problem is that the system wide default folder icon has changed, and I'm sure you'll agree that manually changing every single folder icon on my computer is not something I'd like to try!

I mentioned in my post that the usual method for changing the default folder icon in OS X (the one that will appear whenever I create a new folder) is not working for me. Instead, nearly all my folders now have the blank page as their icon, though some do not.

I've also noticed that both Finder and Pathfinder are showing the Preview icon instead of the icon image, when browsing the /System/Library/CoreServices(etc) folder, or indeed any folder containing files: the images show fine in cover flow, but the thumbnail attached to any file name is the Preview icon.

So I'm wondering if this is perhaps a deeper underlying problem.