I installed new rear brake pads yesterday on my 06 R12RT. Had the same problem. Removed the old pads, AND the new ones wouldn't fit. I remembered reading something about this previously. Searched and found this very helpful information. Spread the caliper out and squirted a little brake cleaner to clean it up. Voila, the pads slid into place.

I really appreciate the helpful servicing tips and info that can be found here.