For all floppies I've tried, the error msg was A:\ is not accessible. The device is not ready.
However, when I used "send to" I got a message along the lines of "insert floppy with volume/address nnnnnn" which led me to believe it was due to an incomplete operation to/on a floppy file.
However, with 2 sons, I just tried to open and close down a couple of word documents that I knew the younger had been working on, on that computer. Having done that, I seem to be able to copy those documents to floppy. But still unable to read them, so obviously some corruption there.