Outlook hangs and fails to open after a windows 11 update

Anna Tow 20 Reputation points
2026-07-01T09:03:16.5033333+00:00 
UTC Date: 2026-07-01T08:59:16.853Z
Client Id: 
Session: 
Client Version: 20260619010.12
BootResult: fail
Back Filled Errors: Unhandled Rejection: SyntaxError: Failed to execute 'json' on 'Response': Unexpected end of JSON input:undefined|undefined:undefined|undefined:undefined|undefined:undefined
err: Error: 401
esrc: StartupData
et: ServerError
estack: Error: 401
    at 
st: 401
efe: 
reqid: 
cv:

[Moderator note: personal info removed]

Outlook | Web | Outlook on the web for business | Email
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Answer accepted by question author
Jayden-P 26,270 Reputation points Microsoft External Staff Moderator
2026-07-01T09:38:05.35+00:00

Please note that our forum is a public platform, and we will modify your question to hide your personal information in the description. Kindly ensure that you hide any personal or organizational information the next time you post an error or other details to protect personal data.

Hi @Anna Tow

Based on the error message provided, the issue appears to be related to an authentication failure when Outlook on the web attempts to load your mailbox data. This can sometimes occur due to a corrupted session, account mismatch, or a temporary backend issue.

Here's the steps you can try:

  • Close all browser windows and open a new incognito tab and sign back in using your work account.
  • Clear browser cache and cookies.
  • Try accessing Outlook from a different browser (use Edge if you are using another browser) or device. (eg. your mobile phone)
  • If you are using Edge, on the webpage, click the Lock icon on the browser's address bar on the left > Click Cookies > On the popup that opens, remove all cookies one by one, by selecting each cookie and remove the same > Reload the page and sign in again using the credentials.

If the issue persists, please contact your IT administrator of your company and ask them to remove your Microsoft 365 license, wait a few minutes, and then reassign the license

This step helps refresh the mailbox provisioning and associated services, which can sometimes resolve authentication-related failures.

Please try and let me know how it goes.

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

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