There is probably something wrong with the card reader or the card.
Maybe just dirty contacts.
Best thing to do back up your data from the card just in case.
Perhaps when you are 100% sure you have a good backup you could reformat the card.
Or get another card and start fresh.
There are lots of ways to send files, but try sending them again (after backup
).
Less confusing IMO.
For instance you could send them to the card when it is in the computer card reader.
To beat the horse to death, the errors you were getting are basic i/o errors. Calibre uses the computer operating system i/o functions to transfer data.
You were probably doing everything correctly but had bad luck (data read error). I am sure you will get it all done very soon.
Helen