Intenta esto.
function autos ( player, seat, jacked )
local x, y, z = getElementPosition (player)
local auto = createVehicle(583, x, y, z)
if ( seat == 0 and source == auto) then
local accountName = getAccountName ( getPlayerAccount ( player ) )
if ( not isObjectInACLGroup ( "user.".. accountName, aclGetGroup ( "Admin" ) ) ) then
cancelEvent ( )
outputChatBox("No eres Admin.", player, 255,90,0, true)
end
end
end
addEventHandler ( "onVehicleStartEnter", root, autos )