Cannot cast from source type to destination type? C#

Here's the void that's causing the error

     public void SpawnUnit(Transform unit, string name, Vector3 pos, Quaternion rot, int pop) {
         if((rsm.playerResources[ResourceManager.ResourceType.CurrPOP] + pop) <= rsm.playerResources[ResourceManager.ResourceType.MaxPOP]) {
             tempObject = (GameObject)Instantiate(unit, pos, rot);
             tempObject.name = name;
             rsm.addResource(ResourceManager.ResourceType.MaxPOP, pop);
         } else 
             Debug.Log ("Too much population shit");
     }

Here's my script calling this.

     DummyScript ds;
     public Transform worker;
     Transform myTransform;
     // Use this for initialization
     void Start () {
         myTransform = transform;
         ds = GameObject.FindGameObjectWithTag("ScriptManager").GetComponent<DummyScript>();
         for(int i = 0; i <= 5; i++ ) 
             ds.SpawnUnit(worker, "Worker", myTransform.position, myTransform.rotation, 1);
     }