Unable to use server commands on Nightly Build

I am running DH on a modded forge 1.2.0.1 server using what I believe to be the most recent nightly build. I am experiencing some lag while playing and I wanted to use some of the server commands to try and see if I can make any improvements. When I try to use any of the commands I get an error message. I am using the same nightly build client side as well. Any idea what I should do to resolve this?