This is a known issue from the May 1, 2026 MSAL update — same root cause for BC and F&O.
Cause: an update to the Microsoft Authentication Library (MSAL) is causing timeout and sign-in loop issues in the Dynamics Office Add-in. Started around 1 May 2026. Microsoft has a known-issue ticket open: https://admin.powerplatform.microsoft.com/support/knownissues/6355973
Fix order — try in this sequence:
Clear the Wef add-in cache. Close Excel completely (kill any leftover EXCEL.EXE in Task Manager), then delete the contents of %LOCALAPPDATA%\Microsoft\Office\16.0\Wef. Reopen Excel and try again.
If that doesn't work, also clear the Identity cache. Win+R → paste %LOCALAPPDATA%\Microsoft\IdentityCache\ → delete contents. Then re-sign into Excel itself (File → Account) and reopen the add-in.
Clear the Office credential cache in Windows Credential Manager (Control Panel → User Accounts → Credential Manager → Windows Credentials) — remove anything starting with MicrosoftOffice16_Data: or referencing dynamics.com.
As a last resort, uninstall the Microsoft Dynamics Office Add-in from Excel (Insert → My Add-ins → Manage → Remove), then reinstall from AppSource.
On the EXCEL EXPORT ACTION permission — that controls whether the Edit in Excel button appears in BC, not whether the add-in itself can authenticate. So it's unrelated to this MSAL error. If users can't see the action at all, give them the D365 EXCEL EXPORT ACTION permission set (or include it in their main role).
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Regards
Gregory Mavrogeorgis
