Getting NAN for simple equation

I currently have 7 different PID controllers controlling a simulation, all with different tuning values. They are all coded the exact same aside from variable names and tuning values. The strangest thing is that the latest one I added is giving me NAN despite the simple equation outputting what I would think is a usable value.

Here is my code:

 //Input Values in fixedUpdate
 var dist : float = Vector3.Distance(pathpoint, uavPos);
 var zVel : float = UAV.transform.InverseTransformDirection(GetComponent.<Rigidbody>().velocity).z;

 //Runs through 2 PIDs in fixedUpdate
 var distErr : float= locZError(0, dist);
 var velErr : float = velZError(zVel, distErr);

 //PID with NAN Error
 private var errSumVelZ : float;
 private var lastTimeVelZ : float;
 private var lastErrVelZ : float;
 function velZError(input : float, setPoint : float){
    //input=0.0001448985 setPoint= 181.3836
    var now : float = Time.time;
    var timeChange : float = (now - lastTimeVelZ);
    
    var error : float = setPoint - input;

    Debug.Log(error); // outputs 181.3835
    Debug.Log(timeChange); // outputs 0.01999998
    Debug.Log(error * timeChange); // outputs 3.627666
    errSumVelZ += (error * timeChange);
    Debug.Log(errSumVelZ); //outputs NAN

    var dErr : float = (error - lastErrVelZ) / timeChange;
    
    var Output : float = (.3 * error) + (0 * errSumVelZ) + (2 * dErr);
     
    lastErrVelZ = error;
    lastTimeVelZ = now;
    
    return Output;
 }

What would cause 'errSumVelZ += 3.627666' to create NAN?