Oh, my. Are your configs exactly the same? Is this a new world, or an existing world? Are you upgrading from a previous IC2 version?
Thanks man you already helped me 
for those having the same problem: i still had the old IC2.cfg in /config
after deleting the .minecraft folder and installing everything from the scratch it worked perfectly fine
tl;dr: problem solved, delete config folder or install .minecraft completely fresh
i tried to use the latest IC² addon in multiplayer.
first we tried via installing the addon on both PCs (my friends and mine) and then open it to lan and try to connect.
We get this error: http://i.imagebanana.com/img/roygu71t/error.png
after trying to install IC² to a dedicated server, the server started well, loading IC² but after trying to connect it drops the exact same error as before.
any idea what this causes? is this a bug of IC² (still being beta) or are we doing sth. stupid?
(i already used search but didng get anything usefull)
//edit: i am using magic launcher v1.00
