Intenta esto: 
        panel = guiCreateWindow(473,188,281,381,"Nitro & Car panel by: ScorpVI",false) 
        close = guiCreateButton(203,348,67,24,"Close",false,panel) 
        N1 = guiCreateButton(13,39,86,37,"Nitro x2",false,panel) 
        N2 = guiCreateButton(13,141,86,37,"Nitro x10",false,panel) 
        N3 = guiCreateButton(14,90,86,37,"Nitro x5",false,panel) 
        Infernus = guiCreateButton(15,197,237,34,"Infernus",false,panel) 
        dumper = guiCreateButton(18,287,237,34,"Dumper",false,panel) 
        bullet = guiCreateButton(16,241,237,34,"Bullet",false,panel) 
        Imagen = guiCreateStaticImage(118,54,145,110,"images/mtalogo.png",false,panel) 
         
         guiSetVisible (panel, false ) 
         
--Esto lo mantuve aunque corregí un error con respecto al nombre. 
function open () 
guiSetVisible(panel, true) 
showCursor(true) 
end 
bindKey("F2", "down", open) 
  
  
function Exit () 
  
guiSetVisible (panel, false ) 
showCursor ( false ) 
  
end 
  
function infernu() 
Jugador = getLocalPlayer () 
x,y,z = getElementPosition (Jugador) 
createVehicle ( 411, x + 2, y, z + 10 ) 
end 
  
  
function dumpe() 
Jugador = getLocalPlayer () 
x,y,z = getElementPosition (Jugador) 
createVehicle ( 406, x + 2, y, z + 10 ) 
end 
  
  
function bulle() 
Jugador = getLocalPlayer () 
x,y,z = getElementPosition (Jugador) 
createVehicle ( 541, x + 2, y, z + 10 ) 
end 
  
  
function Nitro1() 
triggerServerEvent ( "onNitroo1", getLocalPlayer() ) 
end 
  
  
function Nitro2() 
triggerServerEvent ( "onNitroo2", getLocalPlayer() ) 
end 
  
  
function Nitro3() 
triggerServerEvent ( "onNitroo3", getLocalPlayer() ) 
end 
  
        addEventHandler ( "onClientGUIClick", close, Exit, false ) 
        addEventHandler ( "onClientGUIClick", Infernus, infernu, false ) 
        addEventHandler ( "onClientGUIClick", dumper, dumpe, false ) 
        addEventHandler ( "onClientGUIClick", bullet, bulle, false ) 
        addEventHandler ( "onClientGUIClick", N1, Nitro1, false ) 
        addEventHandler ( "onClientGUIClick", N2, Nitro2, false ) 
        addEventHandler ( "onClientGUIClick", N3, Nitro3, false ) 
 
Muchas gracias Alexs me ayudaste mucho  , me funciono perfecto