First, thanks for yours replies guys ! I haven't got the script here because it's on computer at work... but it has no "exit" because it runs every time, like an antivirus program. Endeed, it's a program to tile windows, fixe others at the top, etc. I can imagine that the crash of my program appears when I want to resize a window that is not responding (but his process is still there). We can understand behind this, that it's NOT a "normal case". A "normal case" is : the process exists or it doesn't exist, we can verify his state before running the function (resize for example). A zombie process or a process that is not responding is NOT a "normal case". You understand ? So I suppose that we can find a function "ON ERROR" that stops the resize function when it happens in order to keep my program alives, but how can we do this with autoit? PS : sorry for my bad english, I'm french.