Sadly, the fantastic integration between Gephi and Neo ended post v0.9 
I know this thread is old'ish, but I just wasted a ton of time trying to figure out how something I'd used in the past wasn't working (it'd been a while since I last needed a Gephi/Neo partnership). This Neo webpage (a dead-end), has a comment at the bottom alluding that Gephi has said this on some blog post of theres. I've not found that but I'm pretty sure that makes sense given the kind of errors I was getting and I know how this works and have used it a ton in the past - key word: past
You can get this working if you go back a version (<0.9) but it seems better to look at updating the plugin if someone has the time/skills.
HTH
PS!!! I'm excited to say that I did some digging after I posted this and found that THERE IS A NEW PLUGIN on Git. Find it here! I've not used yet but I will soon. Just from the repo's README, I'm very optimistic.