client-sided outputChatBox does not have a 'visibleTo' param, also there is no need for onClientResourceStart.
local mRed = 255
local mGreen = 255
local mBlue = 255
local theMessages = {
'Message 1',
'Message 2',
'Message 3',
'Message 4',
'Message 5',
'Message 6'
}
setTimer ( outputChatBox, 1000 * 60 * 5, 0, theMessages [ math.random ( #theMessages ) ], mRed, mGreen, mBlue, true )