He never precached the sound:
Code:
emit_sound(targetid, CHAN_WEAPON, "sound/punch.wav", 1.5, ATTN_NORM, 0, PITCH_NORM );
Add this function:
Code:
public plugin_precache()
{
precache_sound("punch.wav")
}
Also I think you should remove sound/ from emit_sound, I'm pretty sure it already assumes you're in the sound dir.
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