Outlook Error Codes

How to Fix Outlook Error 1001 When Microsoft 365 Will Not Sign In

Khadija Khan Oct 12, 2026 872 views

Question details

Users are unable to sign into Outlook or other Microsoft 365 apps due to an Error 1001 prompt.

How to Fix Outlook Error 1001 When Microsoft 365 Will Not Sign In

Product: Microsoft Outlook
Device & OS: Windows
Scenario: Attempting to sign into Microsoft Outlook after a recent password reset or reinstalling the application.
Observed behavior: Outlook displays a 'Something went wrong [1001]' message and gets stuck, failing to complete the sign-in authentication process.

Before you start

Ensure that you have completely closed all Microsoft 365 applications, including Word, Excel, Teams, and Outlook, before modifying any system folders.

Solution 1Recommended

Move Microsoft Authentication Cache Folders

Clear corrupted login tokens by moving the OneAuth and IdentityCache folders out of the local AppData directory.

This solution works best if the error is isolated to Microsoft Outlook. By removing the existing cache folders, you force Outlook to generate fresh authentication files during the next sign-in attempt.

Close Microsoft Applications

Make sure Outlook and all other Microsoft 365 apps are completely closed.

Open Local AppData Folder

Press the Windows Key + R to open the Run dialog. Type '%localappdata%\Microsoft' and press Enter to open the directory.

Locate Cache Folders

Find the folders named 'OneAuth' and 'IdentityCache' within the Microsoft folder.

Move Folders to Desktop

Cut and paste both the 'OneAuth' and 'IdentityCache' folders onto your Desktop to serve as a temporary backup.

Relaunch and Sign In

Open Microsoft Outlook and attempt to sign in again. The application should now bypass Error 1001.

Move Microsoft Authentication Cache Folders

Folder Restoration: If the issue persists, you can restore the folders from your Desktop back to their original location. However, do not overwrite any newly created folders.

Solution 2

Use Outlook on the Web Temporarily

If you need immediate access to your emails while dealing with desktop client issues, use the browser-based version.

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Frequently Asked Questions

What causes Error 1001 in Microsoft Outlook?

Error 1001 is typically caused by corrupted authentication tokens or cached identity files. This frequently occurs after resetting your Microsoft 365 password or reinstalling the application without clearing older data.

Can I simply delete the OneAuth and IdentityCache folders?

Yes, deleting them will force Outlook to recreate fresh authentication files. However, moving them to your desktop is highly recommended as a safer approach, providing a backup in case you need to restore the original files.

What should I do if Error 1001 appears in Word and Excel too?

If the error occurs across all Microsoft 365 applications rather than just Outlook, it generally points to a system-wide or tenant-level authentication problem. In this case, you should follow Microsoft's official guidance for Error 1001 or contact your organization's IT administrator.

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