[HighFlyer]

First of all, uncomment the forward. Add stock before the function if you haven't so it looks like this.

Код:

stock IsPlayerInArea(playerid, Float:minx, Float:maxx, Float:miny, Float:maxy) 
{
    new Float:x, Float:y, Float:z;
    GetPlayerPos(playerid, x, y, z);
    if (x > minx && x < maxx && y > miny && y < maxy) return 1;
    return 0;
}

And I assume you have IsInPlayerArea defined somewhere again, Ctrl+F, search for it, and remove it.