After spending 3 days trying to align my rear disc brake caliper (Juicy 5) I was starting to give up and call CPS a failure. I then proceeded to try one last time and holy hell, I found out that every time I tried to "realign it" the pads still didn't rub, it was the adapter that was rubbing with the disc all throughout. Now, what does this mean? Will I need a new frame? Can something be done to the disc tabs (maybe grind some of it off)? Can an LBS do this for me? How much will it cost?

Sorry for so many questions but I'm really pissed and I don't know what I'll do if I can't fix the rear tabs.

If they haven't been already, you should be able to get the tabs faced (ground off square) at a well-equipped bike shop.

your disc tab should be grounded ONCES in its frame life to aline your disc brake caliper properly. Get a good bike shop that has the proper tools to do it tho. Infact, many placeds of the frame (headset face, and bb) area should be faced as well to give it a nice flat service for installation, best performances, and last longer. I have had the same problem myself. Your fork disc tab should be grounded too if you have front disc brake.

Take some sandpaper and sand down some of the paint. You can get a shop to face it but sanding has worked on all my bikes. A even hand and a good eye and you can do this without any issues. If you see it is REALLY out of whack and washers aren't working your tabs may be misaligned.