Went to the local grocery store for a few items.  Since it was a hot day, I decided to take the Box with the top down.  Made my purchases and was away from the car for about 2 minutes.  When I came back, inserted the key, it would not turn!  I said to myself, self' OH CRAP".  After a whole bunch of Sailor words your mother would not want to hear and a lot of jiggling the key around, it worked.
What would cause this???  If it happened once, it's going to happen again.  Any thoughts, corrective actions?