[Kh4led]

pawn Код:

dcmd_gps(playerid,params[])
{
        #pragma unused params
        if(!IsPlayerInAnyVehicle(playerid)) return SendClientMessage(playerid, COLOR_ERROR, "[GPS]:You must be in a vehicle to use this command.");
        if(IsPlayerInAnyVehicle(playerid))
        {
          SendClientMessage(playerid, COLOR_GREEN,"[GPS]:You have turned on your GPS.");
          ShowPlayerDialog(playerid, DIALOG_GPS, DIALOG_STYLE_LIST, "GPS:", gpsstr, "Choose", "Cancel");
        }
        return 1;
}

No compiling error, but Dialog doesn't seem to be working.

EDIT: You also forgot to add

pawn Код:

GPS_Activated[playerid] = 1;

under GPS Command.
and ResetVariable.