My best guess is that his blockoff is keeping the piston from going all the way back into the caliper, because the little peg that comes out the side of it is hitting the blockoff. I had the same problem when I installed new rear pads and a moose blockoff plate. I had to dremel out some of the material from inside the blockoff plate for it to work, you just have to be careful because you don't want to go all the way through it.