Office 365 Backup Failed (403 Forbidden)

Userlevel 1

I’m currently running the 30-day trial version of Office 365 backup ( and everything has been running well for the last 10 days or so.   I have the software set up to run every 8 hours for a whole organization backup.


Out of the blue, last night, the backups started failing with “Access denied.  The remote server returned an error: (403) Forbidden”

The admin password is the same and Azure AD shows the login for the Veeam account as successful.  I’ve checked our Office 365 Health panel and see nothing new that might impact the backups. 


I’m running a backup to a local repository and have rebooted the backup server and the proxy server.  I have plenty (4.8+ TB’s) of storage available on the repository.


I went into the Organization setup and reentered the credential info and all of the checkboxes came back as successful.


Has anybody else encountered this issue or does anybody have any hints for how to alleviate it?


Userlevel 1

Well, that was easy….

I checked the proxies and realized the proxy I was using was on an older version.   I upgraded that proxy and it looks like all is working properly again.

Userlevel 4

Same happened to my setup on 5th/6th May 2021.  Working fine, then stopped working.  Solution was to upgrade the proxy. 

Userlevel 7
Badge +14

There's a rather new KB article which describes this problem:

Interestingly the patch is already out since April and you ( @rh0926 ) were already using this version. Perhaps the proxy didn't get updated by itself?

Userlevel 4

I saw that article but looking at my setup I found I was already on the latest version so it was no use to me.  My case was the same as the one described above.  I had a proxy server which was out of date. 

I had another similar instance a few days ago.  This time I found the application had lost the shared secret details.  I had to put them in again and it was fine after that.  I think I’ve seen that happen once before 6 months ago. It just forgets the authentication information. 

Userlevel 7
Badge +21



Just a quick update that Gostev has confirmed in this week’s digest, Microsoft did an API change causing this issue for many. KB article here.