JKB

I have had this mower for years without any poroblems. Started it today, released the brake and when I put the mower into gear with the left and right steering levers, the mower dies. The mower has a safety feature that when the brake is off and I get out of the seat, the mower will die. I tested this with the brake released and the mower keeps running thus it seems that when I release the brake it is not in effect "releasing the brake". The mower still thinks the brake is on so when I stand up it keeps running. Anybody know how to correct this problem?