Pastebin from fml-client-latest.log: http://pastebin.com/0QC3vnbS

Caused by: java.io.IOException: Packet was larger than I expected, found 65536 bytes extra whilst reading packet 63

Yes it's some combination of mods. But it seems when you have enough of these mods it starts exhibiting this error. I'm trying to pin down what exactly the set of circumstances is. Unfortunately that error is not terribly helpful.

@AnodeCathode Do you have Tinkers Construct or Twilight Forest installed along side mekanism? I was seeing that same error last night and it disappeared after I removed both mods from my server.

@bshelden seems to have gotten a client/server connection working just fine.

Closing, as it appears this is not caused by Mekanism.