This might have been mentioned here before...
The other day, before a show, I charged the A10 plugged into my mac. I forgot that it would be connected, so i just disconnected it physically when charging was done. Then the A10 said "The SD card needs to be formatted". I went into panic mode for a second or two...
The solution turned out to be simple. I plugged it back into the mac, waiting till the disks were connected, then ejected them properly before disconnecting, and the error message was gone.
Just thought I would mention this in case anyone ends up in the same situation...
-c