since the 1.5 update i have been having problems with connecting via LAN after testing some possible reasons behind this, i have come to the conclusion that forge mod loader is not compatible with LAN connections right now even if both clients have the same mods. the only error that comes up is an unable to connect to server error, it does not crash the game though. i have come to this conclusion by the fact that i removed forge from my minecraft and i was able to do lan connections.

Same version of FML/Forge?

Yes, i gave them an exact copy of my minecraft jar, which always has forge, and the lan didnt work. We downloaded vanilla and tested it and it worked. Since we also use optifine we added that and it still worked. Meaning that forge was causing the problem.

Just test in my network and lan games work just fine.... Logs and setup information.

Thats an interesting exception, seems to be something to do with the runtime deobfusication.

However, there have been a few fixes to that seince the version you're using. You're on build 608, we are on build 652. So you're quite out of date.

 

Try updating and see if that helps, I will however look into this more.

That log tells me you simply can't connect to the lan server, typically firewalls/whatever else is stopping you.

Its not giving the method not found error, which means that the one you were having before was fixed.

 

As I said, I have tested lan connections, and they work just fine with forge.

Do you have a log of the other computer?

i do not, but i know what its not a firewall issue because we have lan connected the computers multiple times before 1.5 with forge installed. if its not directly a problem with forge ten  do know what could be causing the problem.