Have you had a thorough look at the playfield glass switch to make sure no wires are loose and/or diode (I think it has a diode) as well as making sure that the switch arm is adjusted correctly? If that warning is sounding it isn't recognising that playfield glass switch as being closed.
What do you mean too cold, I think 12 degrees would have been out op temp today. The car was saying 1 degree when I took the young bloke to footy this morning, we had our first good frost as well.
