If you place an IC2 block in the world (on a server) The server will crash and say that Matrix64F.class wasn't found. Clients don't have that problem, so if you're playing SP you're fine.
The solution for that is REALLY simple. When you first lunch your client with IC2 installed, it will download a library called ejml. You can find it under .minecraft\mods\ic2. Copy the jar file (ejml-0.23.jar) to your server's mods folder, and you're done. Restart the server and play as usual.
I'm attaching the crash log I got if you're interested.