Forced Private Start and Struct Name is not valid at this point

I think the error alert telling me to put private void Start is nonsense. It also complains Vector3 is Struct Name is not valid is also nonsense

using System.Collections;
using System.Collections.Generic;
using System.Runtime.InteropServices.ComTypes;
using UnityEngine;
using UnityEngine.coremodule; 

private void Start()
{
for (var i=0;i<col*row;i++)
{
var a = ts.instance();
a.position = Vector3(xst + xs * i % row, yst + ys * (int) (i / col));



}
}