OnTriggerEnter different in Mac / Win

I have a OnTriggerEnter - function wich cals an (Alert) Script.
The Alert Script contains a setting function, wich activates a AlertWindow in OnGUI();

static function alert(str: String): boolean{
	alertTextfield = str;
	alertActivation = true;
 function OnGUI (){
            	GUI.skin = alertSkin;
            	windowRectAlert = GUI.Window (0, Rect(Screen.width/2-260, Screen.height/2 - 50, 500, 310), DoMyWindow, "");	
        function DoMyWindow(){		
        	GUI.Label((Rect(40, 80, 430, 200)), ""+alertTextfield);
        	if(GUI.Button(Rect(200, 260, 100, 30), "OK")){
        		alertTextfield = "";
        		alertActivation = false;

After pressing the OK - Button on Mac Runtime, the Alert disappears; on Win the Alert Window won’t disappear.
It seems, that the OnTriggerEnter works different on Win -Runtime then on Mac.
How can I fix this?


OK, seems to be a problem with the GUI.window.
After replacing GUI.window with a “if(AlertIsOn)” in the OnGUI() everything works fine.