Connection Error While Attempting to Sign Into Desktop Microsoft Applications

Question

1-2 days ago I received notifications that my notes on OneNote were not syncing and that sign in would be required. Upon signing in, I would receive this connection issue. I found that while attempting to sign into the desktop version of any Microsoft product, I run into this same issue. This connection error does not appear when signing into the webpage versions. I have tried signing out/back in on both OneNote and OneDrive, as well as altered my background services related to OneNote. Even after restarting, the issue persists.

Answer 1

Can you go check your Windows Settings > Windows update, and see if you might have  KB5085516 available to install?

KB5085516 was released on March 21st to address Microsoft account sign in issue among some apps caused by KB5079473 https://support.microsoft.com/topic/march-21-2026-kb5085516-os-builds-26200-8039-and-26100-8039-out-of-band-09e85404-1cb6-4ed4-9ca5-3e40d74307b9

Answer 2

The behavior matches known connection and sign‑in issues where desktop Microsoft 365 apps cannot reach the authentication service, even though the browser works.

Use these steps to isolate and fix it:

1. Confirm the issue is the desktop sign‑in channel
   • In Microsoft Edge (not Internet Explorer), go to https://login.microsoftonline.com.
   • Sign in and verify that it successfully redirects to https://www.office.com or the normal landing page.
   • Repeat the same test in an InPrivate window.
   • If either of these fails, the problem is with the local firewall, antivirus, or network environment blocking the sign‑in endpoints.
2. Check for AAD sign‑in errors in Event Viewer
   • Open Event Viewer.
   • Browse to Applications and Services Logs > Microsoft > Windows > AAD > Operational.
   • Look for entries around the time of the failed sign‑in that mention XMLHTTPWebRequest or similar network errors (for example codes in the pattern 0x?AA7????, 0x?AA8????, 0x?AA3????, 0x102, 0x80070102).
   • Matching errors confirm that the desktop token‑acquisition calls are being blocked or timing out.
3. Unblock the required processes locally Ensure that local firewall, antivirus, or endpoint security tools are not blocking the token‑acquisition components used by Office sign‑in:
   • C:\Windows\SystemApps\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy\Microsoft.AAD.BrokerPlugin.exe
   • C:\Windows\System32\backgroundTaskHost.exe
   Add these as allowed/whitelisted processes in any third‑party security software and in Windows Defender Firewall rules if they were previously restricted.
4. Verify network access to Microsoft sign‑in service
   • Confirm that the network (home router, corporate proxy, or ISP security features) does not block access to https://login.microsoftonline.com.
   • Because this address maps to many IPs and services, partial blocking can cause intermittent failures where some devices work and others do not. Remove any specific IP blocks or deep‑inspection rules that interfere with this endpoint.
5. If using roaming profiles or VDI
   • Ensure that no data under %localappdata% is being roamed for the AAD and token broker components, and that the following folders and registry keys are excluded from any profile‑roaming or migration tools:
     • %localappdata%\Packages\Microsoft.AAD.BrokerPlugin_cw5n1h2txyewy
     • %localappdata%\Packages\Microsoft.Windows.CloudExperienceHost_cw5n1h2txyewy
     • %localappdata%\Packages\<any app package>\AC\TokenBroker
     • %localappdata%\Microsoft\TokenBroker
     • HKEY_CURRENT_USER\SOFTWARE\Microsoft\IdentityCRL
     • HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\AAD
     • HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WorkplaceJoin
   • Also ensure the work account’s device certificate (issuer "MS‑Organization‑Access") is not being roamed between devices.
6. Temporary workarounds
   • Until the desktop sign‑in path is restored, use OneNote for the web and other Office web apps to access and edit content.

If, after unblocking the listed processes and confirming network access to login.microsoftonline.com, the Event Viewer still shows AAD network errors at each sign‑in attempt, collect those logs and open a support request so the issue can be further investigated.

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References:

• Connection issues when signing in after updating to Office 2016 build 16.0.7967 on Windows 10
• Can't sign in to Microsoft 365 desktop applications
• Error “Something Went Wrong [1001]” signing in to Microsoft 365 Desktop Applications
• Fix issues when you can't sync OneNote
• Unable to sign into account - says I am not connected to Internet but I am - Microsoft Q&A
• How to fix the issue with MS Office asking you to log in every time you open an Office app - Microsoft Q&A