News

Outlook Crash Error Can Only Be Fixed via Microsoft Support

Microsoft is investigating a bug that causes the classic Outlook email client to crash immediately upon launch. At present, the issue can only be resolved with assistance from Exchange Online support.

Who Is Affected

According to a recently published Microsoft document, the problem impacts Microsoft 365 customers using the classic Outlook client on Windows.

On affected systems, users encounter an error message stating that Outlook cannot start and that the attempt to log into the Exchange account has failed.

Microsoft’s Response

The company has not disclosed the root cause of the bug, noting only that it may occur “for various reasons.” Affected customers are instructed to open a support ticket via the Microsoft 365 Admin portal, where the Exchange Online support team can apply service-side changes to resolve the problem.

While the investigation continues, Microsoft is asking impacted users to verify the issue by running a Fiddler trace and checking for the error code:
LID: 49586 - Authentication concurrency limit is reached.

Troubleshooting Guidance

Microsoft has also pointed users to its general troubleshooting documentation for Outlook errors such as “Cannot start Microsoft Outlook. Cannot open the Outlook window.” Recommended steps include:

Starting Outlook in safe mode and disabling add-ins
Creating a new Outlook profile
Repairing Outlook data files
Running the /resetnavpane command

Workarounds

Until a permanent fix is available, affected users are advised to temporarily switch to the new Outlook for Windows or use Outlook Web Access (OWA) to access their mailboxes.

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Who Is Affected

Microsoft’s Response

Troubleshooting Guidance

Workarounds

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