no permissison to copy the book

I have read the previous discussion but I still have an e-book from the library which I cannot copy to my kobo. I have tried turning the computer off then on again; cancelling the download from the library and doing it again; dragging the book across as well as doing it by the mouse; I have also downloaded and copied another book just to make sure I was doing everything correctly. I have not had this trouble before. ​Aunty Marg