Not sure, I'm no pro at this lol
All I know is that Windower updated when I logged on initially, and I got the exact same error you listed(same line and everything), I had the gearswap.lua open, deleted the 'update' folder logged back on, had an odd message(was a result of having the gearswap.lua open), still wasn't working, so I closed the gearswap.lua, deleted the 'update' folder again, re-logged and everything was working fine, error was fixed.