BTW, I don't see the element myGate, So i guess that you've got a object scripted in the serverside file.
--server
function openMyGate ()
moveObject ( myGate, 500, -781.20001220703, 2624.8000488281, 104.09999847412, 0, 0, 0 )
triggerClientEvent ( "playsound", getRootElement())
end
addCommandHandler("opengate",openMyGate)
--client
function sound()
sound = playSound3D ("opengate.mp3", -781.20001220703, 2624.8000488281, 104.09999847412, false)
setSoundMaxDistance ( sound, 10 )
end
addEvent( "playsound", true )
addEventHandler( "playsound", getRootElement(),sound )
meta:
<script src="server.lua" type="server" />
<script src="client.lua" type="client" />
<file src="opengate.mp3" type="client" />