Cannot access ACSM files - Connection error detected

Hello,

I am running ADE 4.5.12 on a Mac, and trying to access an ACSM ebook.

However, when opening the ACSM file into ADE, after a few minutes idling it says "Connection error detected" and it is not able to download the ebook.

I have tried several fixes but nothing worked:

- De-authorising and re-authorising the computer

- Connecting to a different WiFi

- Reinstalling ADE

- Date/Time set correctly

- Allowed all incoming connections from Firewall

- Tried with different ACSM files.

Is there any way to understand where the problem is? 

Thanks