this is a malfunction in auto select, very often righting itself, but if you have had it a while get it scanned,
Here is a snippet from a Google page.
This has happened to me too - dont worry - believe it or not its the position of your auto-selector that causes the problem. Normally this fault indication means as the handbook puts it "an incident in the auto transmission". As you say, it re-set when you turned the car off - if there was a fault it would go into limp home mode and contiue to warn you. The first time it happened to me I was scared (expense!!!), the "fault", is actually you being a little too gentle with the lever!
Although in "Drive" the position switch isnt quite engaged and the electronics dont know whats going on so they panic - meanwhile the car drives perfectly normally (except the warning turns you grey). Yours went into limp home mode. It can actually be "made" to show this fault by slowly and very carefully moving from Park into Drive untill the lights alternately flash!