thanks dwanthny, The kindle instructs to eject if one wishes to read or shop while charging. I have tried it both ways ejected and not ejected. No clear pattern. It seems although exporting from calibre to kindle gives this error message, I can send from kindle into calibre just fine.
I thought I had some kind of malfunction in USB cable or port on the kindle as the eject screen comes and goes if the device is moved. Others have told me this is common in usb devices being charged through the computer?
If the connection is faulty I would think I could not send from kindle to calibre either?
I can drag and drop so I can work around this but it is a puzzle.