License Error (Windows)

I get books from my local library via acsm files and this has been working fine for years.  For the past week I've been getting the following error:

Unable to download

Error getting License. License Server Communication Problem:

E_LIC_LICENSE_SIGN_ERROR

I have de-authorised and re-authorsised ADE several times, uninstalled and reinstalled several times, including deleting all directories in my profile and the Adept key in the registry.  Nothing is working.  I've been re-downloading the acsm files each day as I realise that they expire.

I'm using ADE 4.5.11.187303 on Windows 11.

Any other ideas?