could be that the file is 'read only' could be that you have poser open and the file is in use could be that you have given it a wrong name (spaces count) could be that you need to reboot your computer occasionally could be that something else is happening on your system at the same time that causes a hiccup and a call is missed lots more top three would be the 'read only' one poser is using it and the need to reboot