Hi and Welcome!
The error message "Read Error" is no good. It means, your device can not properly access the media inserted. Perhaps, just reinserting might help.
I am guessing you talk about a digital camera, which can't read the inserted flash memory chip. Get a card reader and see if you can access the data and then back them up as soon as possible.
If you are done with the backup (double check), then you can try if formatting the card in the camera makes the card useable again (all data on it are gone, of course).