Stuck on black ops :(?

well the mission objective is : escape with Dr.Clarke i think and im at the point where im on the rooftops and i have just slid down from a roof and then in slow mo i had to shoot 4 guys. im stuck in this little square as all the doors are closed, i cant break anything and cant jump on anything. i think it has something to do with the gate but its closed :( what the heck do i have to do??? :(