Lever problem

[WLN73]

Hi .... excuseme for my bad english first

I have a little problem with a lever .... im tryed to turn on/off a light .... all working but the lever moves by itself from all sides .... as if trembling ...
This is the script i maked:

void OnEnter()
{
SetEntityPlayerInteractCallback("switch1", "func1", true);
}

void func1(string &in EntityName, int alState)
{
if( alState == -1)
SetLampLit("light1", false, true);
if( alState == 1)
SetLampLit("light1", true, true);
}

What did I do wrong? why the lever goes crazy???