diff -up widelands-build17-src/src/ui_basic/window.cc.crash-on-messagebox widelands-build17-src/src/ui_basic/window.cc

--- widelands-build17-src/src/ui_basic/window.cc.crash-on-messagebox	2012-04-23 11:46:49.000000000 +0200

+++ widelands-build17-src/src/ui_basic/window.cc	2012-06-25 14:00:05.677491646 +0200

@@ -252,12 +252,15 @@ void Window::move_inside_parent() {

 */

 void Window::center_to_parent()

 {

-	Panel & parent = *get_parent();

+	Panel * parent = get_parent();

+

+    if (!parent)

+        return;

 	set_pos

 		(Point

-		((static_cast<int32_t>(parent.get_inner_w()) - get_w()) / 2,

-		 (static_cast<int32_t>(parent.get_inner_h()) - get_h()) / 2));

+		((static_cast<int32_t>(parent->get_inner_w()) - get_w()) / 2,

+		 (static_cast<int32_t>(parent->get_inner_h()) - get_h()) / 2));

 }