I have found the cause "Please note that after SetLayeredWindowAttributes has been called, subsequent UpdateLayeredWindow calls will fail until the layering style bit is cleared and set again." from http://msdn2.microsoft.com/en-us/library/ms632599.aspx#layered
But I still can't use winxpgui.UpdateLayeredWindow, Now I am using ctypes to enable calling UpdateLayeredWindow, and this works. -- http://mail.python.org/mailman/listinfo/python-list
