Outlook web 500 error System.FormatException

Question

I am experiencing a 500 error when trying to access Outlook web. Outlook clients on my office PC and Android phone are fine. The problem occurs on a client's PC (Edge on Windows 10) and on my mobile browser (Edge on Android).

I am the global admin for my company's Microsoft 365 tenant. Outlook web was working OK on Friday on my client's PC. Using Outlook web on my client's PC to connect to my client's M365 tenant works fine, so the issue appears to lie with my tenant or user account. I don't think I've made any chances to either of these recently. I've checked my user account and all email apps are allowed.

clientIPAddress nnn.nn.nnn.nn
X-ClientId: 10CC159AEE90465B92091703F07E3823
request-id 5d37f709-4e7f-b6fe-9839-010beee8b028
X-OWA-Error System.FormatException
X-OWA-Version 15.20.4778.18
X-FEServer DB3PR06CA0030
X-BEServer DB9P191MB1771
Date:20/12/2021 01:14:35

Answer 1

Hi @Neil Benson

Is your environment a cloud only one, no on-premsies Exchange server?

Have you tried using other browser and private mode to access OWA? Do you have other admin roles for this account, if yes, remove them temporarily and only keep Global Administrator.

In addition, you could also check the Service health in your admin portal to see if any issue occurs
https://admin.microsoft.com/Adminportal/Home?source=applauncher#/servicehealth

If the suggestions above are helpful to you, it's also suggested to open a service request to o365 backend to get further information what may caused this issue: Get support

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Answer 2

Check this thread for help - https://learn.microsoft.com/en-us/answers/questions/394801/500-error-on-login-to-outlookoffice365com-systemfo.html

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Please mark as "Accept the answer" if the above steps helps you. Your suggestion will help others also !

Answer 3

I had the same issue

Run the New-MoveRequest -Identity "user@Company portal .com" to move the mailbox to a new database

It fixed my issue but note the disclaimer by MS on https://learn.microsoft.com/en-us/powershell/module/exchange/new-moverequest?view=exchange-ps

You can use this to check the progress of the move request
https://learn.microsoft.com/en-us/powershell/module/exchange/get-moverequest?view=exchange-ps

Hope this helps others