Problem with scripting monsters

[The chaser]

I've tried the script:

void OnStart()
{
AddEntityCollideCallback("Player", "ScriptArea_1", "ActivateMonster", true, 1);
}

void ActivateMonster(string &in asParent, string &in asChild, int alState)
{
SetEntityActive("servant_grunt_2", true);
}

void OnEnter ()
{

}

void OnLeave()

{

}

It doesn't work. I think it's ok, what could be wrong?