make sure you connect to servers that have m3l3_coop running
the reason the tank moves, and crashes you, is because you are trying to run a server with the original bsp and scr file (original map file from the singleplayer demo)
use the new one, it should be called m3l3_coop and can be called using the new pak file (make sure you use the new shortcut)
if your readme does not say "version 2" at the top, redownload the mod from here:
www.mohmatch.com