Forum Discussion
SharePoint guests can't login even with correct permissions
A client is unable to use SharePoint with guest users. When attempting access, an error message is displayed with no specific details—only a generic "unknown issue" notice. Error Message Displayed: ...
I’ve had this happen a few times with external users and it’s usually not the permissions in SharePoint itself, it’s the guest account in Entra/AD causing the trouble. Even if they show up with the right permissions, SharePoint might still be pointing at an “old” identity or the invite didn’t get redeemed correctly.
What’s worked for me is:
- Remove the guest everywhere (site permissions, M365 admin, and from Entra including the recycle bin).
- Re-invite them fresh, and tell them to open the invite in a private/incognito window so it doesn’t grab cached credentials.
- Double-check that they’re signing in with the same email you invited.
If you’ve got conditional access policies running, that can also trip them up, so worth checking those too.
Not the most fun fix, but usually after a clean re-invite things start working again.