Thanks for the reply.
Thought so, I think I'm having version issues then. No need to worry about client end, it's only a server for a few of my friends so shouldn't be too much hassle to get things sorted at their end.
Sorry if this has already been posted somewhere. I couldn't find it.
If I wanted to add iron chest to the tekkit server would I just install the plugin in the server and add the mod to the clients of the people who play on it?