Hiding Objects Not Working (Active/Enable)

The following script is attached to the root node of my soldier object in the asset hierarchy:

function Start( )
{
    toggleMarker( false );  
}

function OnMouseDown( ) 
{
    if( GameState.activeUnit == this )
    {
        toggleMarker( false );
        GameState.activeUnit.animation.Play( "staying" );
        GameState.activeUnit = null;
        GameState.travelTo = null;
    }
    else
    {
        var clip = Resources.LoadAssetAtPath("Assets\\Sounds\\roger.wav", typeof( AudioClip ) );
        AudioSource.PlayClipAtPoint(clip, transform.position);
        GameState.activeUnit = this;
        toggleMarker( true );
    }   
}

function toggleMarker( isOn ) 
{
        // gameObject.Find( "SelectUnitMarker" ).active = isOn; 
    Find( "SelectUnitMarker" ).active = isOn;
}

I've tried off the transform as well, none of these appear to work - what is the problem here, it seems a pretty trivial operation. All I want to do is get an object, attached to my soldier (an arrow to indicate if they are active or not) and toggle its visibility.

In the commented code, you have gameObject.Find() in lower-case, and it should be upper-case to indicate you are calling a Class function. Also, it's good practice to store a GameObject reference, rather than repeatedly calling Find(). Try this code:

private var uMarker : GameObject;

function Start() {
    uMarker = GameObject.Find("SelectUnitMarker");
    if (uMarker == null)
        Debug.Log("uh-oh");
}

function ToggleMarker(isOn) {
    uMarker.active = isOn; // Method 1.
    uMarker.transform.renderer.enabled = isOn; // Method 2.
}

If you use Method 1, and the GameObject has children that you also want deactivated, you want to use SetActiveRecursively().

Another way to just make it invisible, as opposed to entirely deactivating it, is Method 2 listed above, turning off the Renderer.

And Eric5h5 is right, if the GameObject is a direct child of the soldier object, you can use transform.Find(). If it's further down the chain, say a grandchild, you have to give it the full pathname, though - see the link for example.

Update - I slightly mis-interpreted the question, I saw the gameObject reference, and missed the part about the object being attached. So to add:

GameObject.Find() - searches the entire scene. Returns a GameObject.

transform.Find() - searches for direct children, or grandchildren if you give a full path name. Returns a Transform.

Maybe you mean transform.Find?