I can speak only a little English! So, the problem is : Why the MouseWheel of UDF works only for one child gui and only once? Please help me! Thanks a lot! #include <GUIConstantsEx.au3> #include <WindowsConstants.au3> #include <GuiScrollBars.au3> #include <ScrollBarConstants.au3> #include <SendMessage.au3> Global $aSB_WindowInfo[1][8],$Form[6] $hGUI = GUICreate("Test", 400, 300) $button0 = GUICtrlCreateButton(" 0 ",5,5) $button1 = GUICtrlCreateButton(" 1