Hi Yogesh,
That message means it read a file but the file it read was of a size that did not match what it should be. I’m not sure how that would have happened. Can you see if reading the device ID works? The call is getDeviceId(). It should return the device ID that is on the sticker of your mDot.
Is your application using the file system? Is the file system not working for you?
Kind regards,
Leon