ERROR Message "UNABLE TO OPEN" and "E_IO_Cannot_Open"

Trying to download 6 ebooks from Hive and I can download the acsm file but when I click that I get an error message "Unable To Open" and "E_IO_Cannot Open." The computer is authorised and uses Win 7 with ADE 3.  I tried ADE 4 but no better.  I have an older PC using Vista and ADE 2 and that will download okay but it is constantly being used so it is not convenient.  Does anybody know what's wrong?  Thanks.