Sorry I have been busy the past few days. Just having another look at this problem.
What I am really mostly having problems with, is opening books that I have borrowed from the library on my Macbook. These come from the library in .ascm format, and in my Macbook the file is greyed out and I can't click on it.
Also, when I open ADE in my PC and plug the Kobo into the USB, the Kobo shows up on the left-hand side of ADE and I can browse all of the books on the Kobo.
However, on my Macbook the Kobo does not show up. I can see "Bookshelves" on the left hand side but the Kobo is simply completely absent. I copied some of the books manually using Add Item to Library, and navigated to my Kobo using Finder. These books do show up now on ADE Macbook. However, the Kobo still does not show up on the left hand side of ADE in Macbook and therefore I am unable to browse the Kobo or add new books to it using ADE.
I can't see where to find out which version of ADE is on the Macbook. However it is only recently that I installed it.
So, adding books to the Kobo can be done on the Macbook but only through the Macbook Finder, not through ADE. And if I want to install an ASCM file then it's not possible through Macbook Finder. This file appears to have to go through ADE or it won't work.
I uninstalled ADE and re-installed it using the file from the link you provided. However, there was no change, and the identical problem is still happening.
Thank you for your help.