First off thanks for posting the screenshot, helped me to see what went wrong!

I can see what happened here, you clicked  Write Images to Disk before you clicked the Slice button. It's the fault of the UI, the write button should be disabled until slice is clicked.  I'll update the software to prevent this - or maybe if you click the write before without clicking slice it will automatically slice first? - anyhow, for now, just be sure to click Slice before Write images to disk.