Thanks for your help Franky. My problem seems to be an issue with the name of the skin in the script...
With CAM 0.77, in game the skin for me is called "American Airlines Retro" the folder in the mod is "American_Airlines" and if I use either of those names in my RAT script, it fails.
--Declare local Variables
local b737=RAT:New("RAT_B737")
local b737skins={"Aero Mexico","American_Airlines","SouthWest Lone Star","UPS"}
-- Set Departure Airfields
b737:SetDeparture({"Henderson Executive Airport", "Laughlin Airport", "McCarran International Airport","Tonopah Airport"})
-- Set Destinations
b737:SetDestination({"RAT_AIRLINER_EAST","RAT_AIRLINER_WEST","Henderson Executive Airport", "Laughlin Airport", "McCarran International Airport","Tonopah Airport"})
-- Set Skins
b737:Livery(b737skins)
-- Spawn Aircraft
b737:Spawn(math.random(4, 8))
-- Set Commands
RAT.ATC.messages=false
b737:SetClimbRate(1000)
b737:SetDescentAngle(0.6) RAT Test.miz