Goto your LBS that has a Sram/Avid trained Tech, we were taught this...
Not an easy quick fix...but definitely reasonable for anyone trained on Avid service.
You've overturned your worm gear and jammed it within the piston assembly.
~This can sometimes happen if you're using both the adjuster and lever at the same time, as in twist-twist-toggle-toggle...
The Lever needs to be pulled, along with the worm gear adjuster, and a 1cm wide flatblade (standard #2 or #3) screwdriver used, along with a 6" crescent wrench and very slight force, turned counterclockwise, no more than 1/4 turn, to free up the gear. Replace the adjuster, and lever, and you should be good to go.
If you don't have anyone local, lemme know and I can get you a referral shop. If you're bike was purchased complete, and has a solid service policy, it might be covered under the service policy.
This is a common occurrence with these brakes. Continuously pump the lever, while turning the dial back and forth easily. The dial usually frees in the direction it can turn in.
Technology is my friend.
Thanks, that works.
God bless the Internet, Google search, MTBR, and Jerk Chicken! I ran into this problem just now. Turned a routine pad change into big hassle. Then I remembered MTBR and found this. After about 10 minutes of pumping and wiggling, I finally got it to adjust again. Whew!