I have the same message and like you the Garmin site showed no updates for my unit

.
If you want to get rid of the message you can try the following:
Switch the i3 off, hold down the back button, the roll wheel and then press the power button so all 3 button are depressed.
It'll ask about resetting data - say yes. It resets it to how it came out the box but the message should be gone.
This will reset to factory default, so all your favourites and saved stuff will be gone

. Only you can decide if it's worth the hassle.