HP C4280 Driver issue

Since upgrading to ML a few months ago, I've printed many things on my HP Photosmart C4280. However, every time I go to use the printer I get told there's drivers to download for the printer.

I then get a EULA to agree to, hit agree, and a dialog comes up saying it's searching for the download (all looks Apple-enough, like it's part of Software Update), I then get an error message saying "The software is currently unavailable. You can check for the software later by choosing Software Update from the Apple Menu".

Just seems to happen eternally - the printer appears to be working fine, but something is making the OS think it has to download drivers, which it then errors out on. Any ideas on how to get rid of the message would be gratefully received! It happens in all user accounts, so when my kids go to print, they also get the same sequence of dialogs to go through...

Thanks!