I recently downloaded the IC2 server file for 1.1 and it wont open, it pops up with this error that says: Failed to load Main-Class manifest attribute from C:/Users/Owner/Desktop/server/industrialcraft-2-server_1.70b.jar
How to setup your own IC²-Server: First of all, you'll need to download and setup a normal MC-server. Once that's all working and you tested whether other people can connect, proceed to downloading the necessary components:
Flan's ModLoaderMP Server 1.1 v2.1 SpaceToad's/Eloraam's MCForge Server 1.3.3
Then grab your IC²-server files, HERE. As with the client, just drop it into the mods-folder of your server directory. Done You may now want to start up the server once to generate the config file and then proceed to build awesome Industrial Worlds with your friends.