scooby dancer

I had been having problems with car not starting after being off the road for some repairs, had disconnected battery (reset ecu) about 4 days. when reading ecu from car not starting was giving code 12 (starter switch) although car was turning over, had checked almost everything usual from sensors, coilpacks/plugs, fuel ect... Thinking along the electrical side did some tests but all seemed well ...
SO the solution i came across by accident when i had left my keys with the wife, as i then was using a different key (which happened to be the original ) car started almost straght away !!! The copy key i have has gone faulty since battery being off!!!! Not saying this will be everybodys solution but something to check could save alot of stress/time. Has anyone had,know of or have a veiw on this!!!!!