One of those forehead slap moments. I was trying to think about what might be different between the setups (except for about 3 years of RetroPie development) when I realised the cable/wifi thing.
I'm glad I worked it out, because my next option was to undo the NAS and put everything on the micro-sd, but the one I'm using isn't big enough, so I'd have to get a bigger one and go through the hassle of moving everything over, etc. Glad I don't have to do that.
thanks, I got it working now. After checking all different settings of my router hardware and the powerline adapters, I resetted the powerline / WiFi adapter to factory defaults an reconfigured it. Strange enough, without changing anything, it works now. I guess that it was a problem with the firmware of the powerline / WiFi adapter since the web interface wasn't available on this specific adapter as well.
@GreenHawk84 I'd definitely back things up every now and then (I do it more or less once a month, but it's more because of my lack of availability than anything else), and keep at least two historical backups (in case you backup something that's already broken, you can always revert to a previous safe backup).
I don't update packages nor emulators unless I need to - if it's working and there's nothing new that I really need there, then I don't risk breaking things. The latest thing I've wanted to update for (but still didn't) was several months back when RetroArch launched the lookahead features to reduce input lag. That's one of the key things I'd be looking for. Still, then you read that the latest RA and lr-fbalpha can cause slight frame drops on CPS3 games in certain setups and you struggle to revert those changes if needed.
So, my preference: unless there's a meaningful new feature for you or a critical security patch, I'd stay with what you have that's working for you.
Also, I am a big supporter of keeping the ROMs in a USB drive and the OS in the SD Card. Easier to backup, transfer roms, and also to set up fresh in a worst case scenario.
Thanks for your advise. What I'm trying to archieve it to see the EmulationStation on my laptop screen via ethernet. I don't think that is possible. I tried a vncserver and when i connected with the viewer there was just a grey screen.
I think that's impossible too. I think you need a Desktop Environment for that. And RetroPie has none per default. You might try installin LXDE though. I instaled RetroPie on top of Raspbian and Raspbian comes w/ LXDE per default. If I were you I wouldn't invest much time in it though.