Accord 2006. The battery died on the remote. When I tried to replace it, I couldn't get the screw loose that holds the clam shell together, so drilled it out. Got a new clam shell with blank key, took it to a hardware store and got the key cut.
* New key: the engine turns over but the green key icon flashes and the engine won't start.
* Old key: the engine turns over and starts.
So ... is there something about the car security
that the new key fails to satisfy? I don't see anything that looks like a chip but it might be buried in the plastic I suppose.