Does zone 2 turn on manually from the valve box? If it doesn't, then you either have a leak or a plugged pipe. Can you hear water when you manually turn the valve on?
How are the wire connections protected? Years ago, a lot of installers used regular wire nuts or marettes to join the solinoid wire to the irrigation wire. Some have used a dab of silicone in the wire nut to try to keep the connection dry, or just used electrical tape. These don't work. Irrigation valve boxes are very moist and corrosive locations that will destroy an electrical connection not done correctly. Pull apart the connection and see if the wire has corroded. I've seen corrosion go the length of the valve wire right to the solinoid. The best wire nut is a King DryConn Irrigation connector. They're not cheap, but you have to use a grease filled, protected wire connector, not a silicone connector. Silicone will fail, let moisture in and corode the wire.
http://www.kinginnovation.com/products/irrigation-products/outdoor-wire-connectors-irrigation/
You will need the black/white ones. The website will show you where you can purchase them.
Is the valve for zone 2 in the same valve box as any other valves? Check the wiring. Pay attention to the common wire. If there is another valve in the box, try swapping the wires. If the wire from the other valve works, then it's not the solinoid. If the wire from zone 2 doesn't work on the other zone, then it's your common, or a bad wire.
After you swap, If the wire from the other valve doesn't work on zone 2 then it's your solinoid.
If your old controller picked up the problem with a "System Error" then it propably is your solinoid. What kind of valves do you have? It will probably be less expensive to purchase a new valve (if the same make and model are still available) than the solinoid by itself.
Before starting this take apart the new valve (slowly) and take notice on exactly how it's put together. Springs and diaphrams need to go together properly and in some cases the screw holes have to be a certain way on the diaphram for everything to work.
Remove the wire connections from the old valve and take the top off. Take the guts out of the old valve along with the diaphram. Do the same with the new valve. Replace the guts, diaphram, top, and solinoid from the new valve into the old bottom of the old valve.
If your valve is no longer on the market, you might have a harder time. You might have to replace the entire valve.
Mick