ADE 4.5.10 won't open ANY epub3 files on Windows 8.1

[aklbe]

For the past few days, when I try to open an epub3 file in ADE I now get a generic error message saying "errors were detected" in the file and nothing happens. This is true even for files which were opened with no trouble previously (days, weeks or months ago), both with and without DRM.

I've tried :

- uninstalling / reinstalling ADE

- following a search on this forum, I deleted all the content and subfolders from the Digital Editions folder on my computer

Neither of these worked for me.

Epub2 files still work with no trouble.

I've seen other threads on this forum which appear to concern the same or similar problem on windows10, for example :

ADE 4.5 won’t open any EPUB3 on Win10

Digital Editions 4.5 won't open

unable to open epub3 in ade4.5.6 with windows 7

Help! Adobe Digital Editions Won't Launch. (NB this one is marked "resolved" because they reverted back to v3)

so it seems like this is not a new problem.

[aklbe]

For anyone else experiencing this issue, someone from Adobe Support gave me this solution, which worked :

1. Uninstall ADE.
2. Open Registry Editor by typing regedit in the run command window.
3. Navigate to ‘HKEY_CURRENT_USER\Software\Adobe\Adept’.
4. Right click on Adept and choose delete.
5. Install ADE again and check the issue.

This solution does leave me with another question though which so far I have not been able to get a reply to. I don't understand why a DRM scheme (Adept) would interfere with opening DRM-free files, or what is the relationship between Adept and epub3. If anyone can give me some information about that I would greatly appreciate it.

[defaultjyxbz30gx9ro]

I could solve this by using ADE with administration privileges (ie, with an admin user). In my case, it was due to an "access denied" error, "HttpAddUrl failed with 5" (what the heck is ADE doing beneath?)