I feel your pain--I had the same thing happen to me. Everything was working great last night...Today my 3rd sensor disappeared and now I cannot get it to be recognized. This is honestly making me want to refund this entire purchase
I am also experiencing something similar. my rift worked flawlessly for months. and suddenly when I go to calibrate my sensors I get a hardware error. I hit try again on the screen with the green checks. and all green. soon as I advance past the touch controller binding however I get the error. this renders my rift not useable.