[BullseyeHawk]

As I might suspect, you might be calling three functions too fast. I had this problem too.
Attempt to create a timer to re-skin the NPC. (Don't forget to reset player into the vehicle, unless you want the gameserver to crash.. Or, the players just..)

pawn Код:

forward NPC_ResetSkin(npcid);

public OnPlayerSpawn(playerid) 
{ 
    if(IsPlayerNPC(playerid)) 
      { 
        new npcname[24]; 
        GetPlayerName(playerid, npcname, 24); 
        if(!strcmp(npcname, "Unity_Driver", true))  
        { 
            SetPlayerSkin(playerid, 150); // I'd suggest to move this code to the new function
            PutPlayerInVehicle(playerid, Autobus_BusUnitySf, 0); // I'd suggest to move this code to the new function
            Attach3DTextLabelToPlayer(Text3d_BusUnitySf, playerid, 0.0, 0.0, 0.0); // I'd suggest to move this code to the new function
            SetTimerEx("NPC_ResetSkin", 1000, false, "d", playerid);
          } 
      } 
    return 1; 
}

public NPC_ResetSkin(npcid)
{
   // your code here.
}