Unity Vector 3 not recognized

This is my first time asking a question here, so I'm sorry if there are any mistakes or difficulties.

I am currently using Unity 5.4.3 and I am creating an animation with script.
As a flow, read the value from the sensor of Arduino → Calculate the value → Read the current location of the moving object A → Move A by the calculated value → Draw
It's like this.

We have verified that the sensor values are read and calculated (one line at a time), but we cannot read the current location of A below.
There is a possibility that the Vector 3 model does not exist on Monodevelop, or that A is not recognized, but I am having trouble knowing how to confirm it and what the cause is. Could someone help me?

Here are some excerpts from the program:

public Vector3 poshand;
void Start() {
    poshand = new Vector3();
}

void Update() {
    progressstime+=Time.deltaTime;
    if(progressstime>=0.25){
        portRead();
        progressstime = 0f;
    }
}

public void portRead() {
    if(port1!=null&port1.IsOpen){
        // Arduino sensor reading and calculating values around here (not shown because it is long
       try{
            handmoves(myData_proxensor);
        }catch(System.Exceptione){
            textobj.GetComponent<UnityEngine.UI.Text>().text="Verror";
        }
    }
}
  public void handmoves(intard_parameter) {
    poshand=shakeshand.transform.position;// Error here
    poshand.x - =ard_parameter/5;
    shakeshand.transform.position=poshand;// Error here
  }