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Title:

.xlsm files fail to open with “file or extension not valid” + Excel reports file is opened in another application

Body:

Hello,

I am experiencing a persistent issue where any .xlsm file (including brand‑new test files created locally) fails to open in Excel. Instead, I receive one of the following messages:

“Le fichier ou l’extension n’est pas valide”

“/TEST.xlsm est ouvert dans une autre application. Veuillez fermer ce fichier et réessayer.”

The second message sometimes includes a OneDrive‑style URL:

https://d.docs.live.net//.../TEST.xlsm

However, even after unlinking OneDrive, pausing sync, and moving the file to a fully local folder, the error persists.

The file does not open at all—Excel shows the warning and stops.

What I have already tried:

OneDrive / Sync

Unlinked OneDrive from the PC

Paused sync

Stopped OneDrive completely

Moved files outside all OneDrive folders (confirmed local paths)

Deleted OfficeFileCache and WEF folders

Cleared %localappdata%\Microsoft\Office\16.0\OfficeFileCache

Excel Trust Center

Disabled all Protected View options

Ensured macro setting is “Désactiver les macros avec notification”

Opened the Paramètres de blocage des fichiers page

Verified file‑blocking settings and default behaviors

Registry checks

Checked the following keys and they contain correct values:

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Excel\Security

HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Security

Excel resets

Deleted %appdata%\Microsoft\Excel

Restarted PC

Ran excel /safe (same issue)

Ran excel /regserver