My girlfriend has a Scion xD (by Toyota) and recently it stopped running. Can someone help?

The engine would turn over but wouldn't fire. We had it towed to Toyota where they told us there was too much alcohol in the gas tank. They dropped the tank, drained it, and checked the engine components for damage. There were none. Today, I tried to start her car (it still has a gallon of gasoline in it), but it did the same thing as before. My first thought is that there is, once again, too much alcohol in the gas tank. Both times, this has happened when the tank is low. What could be causing this alcohol build up and what can I do to solve this problem?