Have you tried lowering the frequency? 800 might be too much for dual mining. Also, make sure your power supply is supplying enough power. Back before cpuminer could disable the BTC cores my power supply was not powerful enough and the same thing happened, no found shares.
I played with frequency all the way down to 600, still the same results sha256 mines fine all the way up to 900, scrypt no shares being made, psu wise it is hooked up to a 850 thermaltake PC PSU, lots of juice there
What happens if you launch cpuminer only? I was getting those same results... when I get home I will see if I can recreate it.
CPUminer only is the same as when I run both, no share being submitted
Figured out why it is working for me. I have the STM32 Virtual COM Port driver installed, not the WinUSB. So that took care of the scrypt side. To get sha256 to work, I have to be running Slush's mining proxy. I also have some cubes running of the same W7 machine. If I don't fire up the cubes first, cgminer states "No devices detected! Waiting for USB hotplug......" However, i read in a different thread today that in the cgminer batch file to change the switch hotplug=0 to hotplug=5. Just tried it and that makes it hash without needing slush's proxy running. Note that when I changed the hotplug switch my batch file for my cubes failed and I could only mine with the Gridseed, so I changed hotplug back to 0 and just run my cubes first.
That is kind of a jumbled post, I am a noob so take it as it is :p
Hope that helps.
EDIT: (Taken from github) --hotplug Seconds between hotplug checks (0 means never check)