when copying to the KOBO E-reader i get the error message "CE_COPY_NOT_ALLOWED" Can anyone tell me why I get This Message ?

When try to Copy An E-book from the Bookshelf to  My KOBO E Reader I get The Message "Bookname"CE_COPY_NOT_ALLOWED"

I don't understand why I get this Message. Is there any one who got the same message and have a solution.