I just tested it with this and it worked fine. Since the "random" command is a toogle I am turning it off first then enabling random mode.
Code:
weaponarena_randomteamspecific 0
weaponarena off
weaponarena random
Code:
Executing AMX Mod X Configuration File
Scrolling message displaying frequency: 10:00 minutes
[AMXX] ERROR: Weapon Arena is already off.
[AMXX] Weapon Arena will select random weapon on every new round!
P90 Arena was enabled!
L 11/07/2006 - 05:19:49: Server cvar "sv_maxspeed" = "320"
Changed to P90 Arena!
L 11/07/2006 - 05:19:52: World triggered "Round_Start"