Latest Gemini image is 4.0 so make sure that you will be flashing this image and not an earlier one.
I suggest that you would leave the compact flash until you have a working system and then use this thread (for USB Stick, but should be the same with CF) to mount the /var to CF:
http://www.satellites.co.uk/satellit...ash-7000s.html
Also check if you can flash using only the box (need an internet connection) by following this thread (works for DreamBox 7000S and Gemini 4.0)
http://www.satellites.co.uk/satellit...age-7000s.html