Ultrasonic Returning Odd Values

In a recent programing session I have run into an odd error with the ultrasonic sensors. They are returning values of either 0 or 255 no matter where I position it. I have The sensor plugged into digital ports 7 & 8 with port 7 configured as the interrupt and 8 as the out. The variable used is an unsigned integer named Ultra_Front. I have also I attached a screen shot of the code.