had the same problem yesterday with my zg, in a shopping centre car park, thought it might have been radio interference jamming the remote.
All i did to fix it was lift up the 6 tabs which make contact with each half of the remote. - 4 tabs on the circuit board and the 2 on the battery. Then i squeezed it together hard to make contact and it worked. Also scratch off any dirt on the tabs and circuit board contact points so you have a good metal to metal electrical connection.
Also, you can convert to gas for pretty much nothing now, might only cost a couple hundred dollars with government rebate. If you convert to gas the immobilizer is bypassed cos the immobilizer cuts off the fuel line, not the gas