X-Drive Program Error

I’m running the basic x-drive code that I found on a related thread. Here it is

task main()
{
while (1 == 1)
{
motor[frontRight] = vexRT[Ch2] - vexRT[Ch4] - vexRT[Ch1];
motor[backRight] = vexRT[Ch2] - vexRT[Ch4] + vexRT[Ch1];
motor[frontLeft] = vexRT[Ch2] + vexRT[Ch4] + vexRT[Ch1];
motor[backLeft] = vexRT[Ch2] + vexRT[Ch4] - vexRT[Ch1];
}
}

So only the back left motor doesn’t work, and I’m not sure what’s wrong with the code, thanks!

If you set it up so the right joystick controls left right front back Without rotation then this would be a section of the code assuming that if you set all the motors to 127 the robot will go forward :
Motor[backLeft]=vexRT[Ch3]-vexRT[Ch4];
Motor[backRight]=vexRT[Ch3]+vexRT[Ch4];
Motor[frontLeft]=vexRT[Ch3]+vexRT[Ch4];
Motor[frontRight]=vexRT[Ch3]-vexRT[Ch4];