Hello,

Below is the short source code:

var buttonPressed : boolean = false;

function OnGUI()
{
    if (buttonPressed) 
    {
        GUI.HorizontalSlider(Rect(Screen.width * .5 - 100, Screen.height * .5, 200, 20), 5, -40, 40);
        if (GUI.Button(Rect(Screen.width * .5 - 100, Screen.height * .8, 200, 40), "Press Me")) 
        {
            buttonPressed = !buttonPressed;
        }
    }
    else 
    {
        GUI.VerticalSlider(Rect(Screen.width * .5 - 10, Screen.height * .25 - 100, 20, 200), 5, -40, 40);
        if (GUI.Button(Rect(Screen.width * .5 - 100, Screen.height * .8, 200, 40), "Press Me")) 
        {
            buttonPressed = !buttonPressed;
        }
    }
}

My purpose is: vertical slider and 'press me' button shows, after clicking 'press me' button, horizontal slider and 'press me' button shows (vertical slider should disappear), but the vertical slider never disappears.

Thanks.