What would cause my voltswagon jetta to stop running after using ethanol for gas?

Answer 1

The two biggest issues with ethanol as a fuel are:

1. Ethanol is polar and therefore a much better solvent for some materials than gasoline is; this could result in things like seals and tubing swelling or even dissolving if ethanol is used in a fuel system that was expecting a more or less completely non-polar fuel like gasoline.
2. Ethanol is significantly more hygroscopic (absorbs moisture from the air) than gasoline is. Moisture in the fuel is bad for lots of reasons, including potential rusting of some parts within the engine.

Another thing to be aware of is that the energy density of ethanol is about 1/3 lower than that of gasoline, so using ethanol instead of gasoline will result in reduced fuel mileage.
Gasoline mixed with 10% or less ethanol is generally okay to use in modern gasoline engines. (Consult your owner's manual to be sure.) Gasoline with more than 10% ethanol can cause problems in vehicles not specifically designed for it (Flex-Fuel Vehicles). FFVs generally state the maximum percentage of ethanol they're prepared to handle; this usually takes the form of a code like E85 (up to 85% ethanol, with the remainder being gasoline).
I don't know specifically what your Jetta was designed to handle, but it's likely some problem related to the above.