I have this error:

******* script runtime error *******
cannot cast undefined to string: (file 'files/zom.gsc', line 1770)
self setWeaponSlotWeapon("primary", self.pers["weapon"]);
*
called from:
(file 'files/zom.gsc', line 1737)
self GiveWeapons();
*
called from:
(file 'files/zom.gsc', line 798)
self PlayerSpawned();
*
called from:
(file 'files/zom.gsc', line 1424)
spawnPlayer();
*
called from:
(file 'files/_zommenus.gsc', line 966)
self [[level.weapon]](response);
*
started from:
(file 'files/_zommenus.gsc', line 82)
self waittill("menuresponse", menu, response);
*
************************************
********************
ERROR: script runtime error
(see console for details)
(file 'files/_zommenus.gsc', line 82)

********************
----- Server Shutdown -----
Sending heartbeat to cod2master.activision.com
==== ShutdownGame ====
Going to CS_ZOMBIE for
0: EXE_DISCONNECTED
---------------------------

Someone knows how to fix it?

yes, as you can see the self.pers["weapon"] is undefined.

I suspect this is a home-made zommod. You are trying to let the zoms spawn without a weapon, and didnt bother to fill the self.pers["weapon"] var.

Else, this is a bad zommod.

You should post your scripts if you want help with it. Debugging code is impossible when we can't see it, we can only make guesses at what might've went wrong.