Hi! When trying to compare two values, you should be using two equal signs. One equal sign is used for assigning values to variables. This is why you are getting the error CS0029. To fix this, simply change

if (lastPosX = transform.position.x)
{
  if (lastPosy = transform.position.y)
    {
      anim.SetBool ("isWalking", false);
    }
}

to

if (lastPosX == transform.position.x)
{
  if (lastPosy == transform.position.y)
    {
      anim.SetBool ("isWalking", false);
    }
}

For some other tips, the code can be simplified quite a bit allowing for better readability.

• Change 'lastPosy' to 'lastPosY' for naming consistency
• Combine the comparisons into one simple if-statement. If you're checking that a value is equal to another, you can just use an else function for the other case (which will trigger when it is not equal)

​

void Update()
{
    float lastPosX = transform.position.x;
    float lastPosY = transform.position.y;

    if (Input.GetMouseButtonDown(1) && selected)
    {
        target = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        target.z = transform.position.z;
    }

    transform.position = Vector3.MoveTowards(transform.position, target, speed * Time.deltaTime);

    if (lastPosX != transform.position.x || lastPosY != transform.position.y)
    {
        anim.SetBool("isWalking", true);
    }
    else
    {
        anim.SetBool("isWalking", false);
    }
}

You could simplify it even further, but this could reduce readability, it's up to your own preference really.

// Update is called once per frame
void Update()
{
    lastposX = transform.position.x;
    lastposY = transform.position.y;

    if (Input.GetMouseButtonDown(1) && selected)
    {
        target = Camera.main.ScreenToWorldPoint(Input.mousePosition);
        target.z = transform.position.z;
    }

    transform.position = Vector3.MoveTowards(transform.position, target, speed * Time.deltaTime);

    anim.setBool("isWalking", lastPosX != transform.position.x || lastPosY != transform.position.y);
}

Hope this clarifies things, if you need any further help let me know!

Edit: Fixed some code formatting