First try saving to a different folder, it may be something to do with the folder security. Try saving to a usb to see what happens. Also try saving as a different file type. I don't have 11, I have p10 but I would have thought it would be the same. As a work around you could type the name in the first time and copy that then paste it in for the next image and change the last digit. Ill try saving as a tif next time I'm on my Mac an see what happens.