Well Kurt - it could be several things but I'd start with the fuel filter. Has it been changed recently? Temperature swings can also cause condensation in the fuel system anywhere between the tank and the engine. Because water is heavier, it will collect at all the low spots and all it takes is a bit of water to prevent starting. It's always a good idea to keep the tank as full as possible to eliminate the air space where condensation tends to collect. A good full stabilizer helps during the winter months as well.

Good luck with this one. I'm sure you'll get a lot of suggestions.
Glenn