Command Blocks Dont work on my server

i have just updated my server to 1.4.2 and when i try and use command blocks and give it power even when i put a command into it it does nothing and the command doesn't work i really want this for my pvp arena

can anybody help

PS this is on a server made whilst on 1.3.2

http://youtu.be/0uysuqpAvTM

a video showing you they dont work aswell read the video description