Arduino BT set MUX mode, now can not upload

hello guys A few days ago I set my arduino BT to MUX mode, then the arduino BT can not upload anything, so I use another arduino board, and the "arduino as isp" method to burn program to my arduino BT, but it still can not disable the MUX mode, and if I don't use an extra arduino board(as AVR-ISP) I can not upload anything. does someone have ideas? Thanks smiley-roll-sweat