Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Try turning Off the Garmin device.
Take out the microSD adapter.
Wait a few minutes.
Put the microSD adapter back in, firmly.
Turn On the Garmin device again.
Does it now find itself able to read the maps (that I presume are on the microSD card that is read through that microSD adapter) ?