just purchased a 2001 e320.

drove to store locked car with electronic key. went to car unlocked and placed items in back seat. relocked car went into another store. when Icame out and tried to start car ignition would not let engine start. turned over several times.

I know it is being locked out but don't know why it does it.
finally took hard key out of electronic key unlocked doors and it started right off. any ideas on how to keep this from happening?