I have been Battling this problem too, My shield portable works perfectly at home. At home GFE wakes my computer out of sleep mode and I was amazed at how good of gaming experience it was, but when I tried to use it's remote game stream functionality I found that it NEVER worked, it said my PC couldn't be contacted. I used my phone's 4g tethering and connected remotely; I ended up finding that it worked perfectly(when the computer was not in sleep mode), then I put my computer to sleep and tried again. I found GFE software wouldn't wake up my computer( when connecting remotely) and gave me the same error I got when I was not at home. I would say try this, or, you can go to the power setting and disable sleep temporarily and try again. I'm guessing that will work. I still haven't found out why the GFE software won't wake my computer when connection remotely, BUT remote game streaming DOES work for me. Until I can determine why GFE won't wake my computer remotely, sleep mode will remain disabled.
I hope this helps you and others who are experiencing this problem.