//First Forward it
forward AdminArea();

//Then make a new Variable for the AdminArea
new Float:Pos[MAX_PLAYERS][4];

//Then add the Function with a public at the front
public AdminArea()
{
    for (new i = 0; i < MAX_PLAYERS; i++)
    {
        if (IsPlayerConnected(i) && !IsPlayerAdmin(i))
        {
            GetPlayerPos(i,Pos[i][0],Pos[i][1],Pos[i][2]);
            GetPlayerFacingAngle(i,Pos[i][3]);

            if(Pos[i][0] >   xmin    && Pos[i][0] <  xmax	// xmin, xmax
            && Pos[i][1] >   ymin    && Pos[i][1] <  ymax	// ymin, ymax
            && Pos[i][2] > zmin      && Pos[i][2] <  zmax)	// zmin, zmax
            {            	
		SetPlayerHealth(i,0);
                SendClientMessage(i,COLOR_RED, "Logge dich als Admin ein um Zugang zu Area 59 zu haben.");
            }
        }
    }
}

//Then just make a Timer
SetTimer("AdminArea",250,1);