The Hybrid Admin

Seeing error code 99 on your Mac is incredibly frustrating. It usually comes with a message telling you OneDrive could not start, completely cutting you off from your cloud files.

This specific bug happens frequently after a bad software update, especially if you installed the application through the Mac App Store. Here is how to break the crash loop and get your files syncing again.

Fix 1: Switch to the standalone app

The most reliable way to permanently fix this error is to ditch the Mac App Store version. The standalone version downloaded directly from Microsoft is much more stable and bypasses the update bug entirely.

1. Open your Applications folder and drag OneDrive to the Trash.
2. Open a web browser and go to the official Microsoft OneDrive download page.
3. Download the installation package for Mac.
4. Run the installer and sign in with your email address.

Fix 2: Force quit stuck processes

If the app is stuck in a crash loop in the background, you cannot restart it properly. You need to kill the process manually before trying to open it again.

1. Press Command + Space to open Spotlight Search.
2. Type Activity Monitor and press Enter.
3. In the search bar at the top right, type OneDrive.
4. Select any OneDrive processes that appear in the list.
5. Click the X icon at the top of the window and choose Force Quit.
6. Open your Applications folder and launch OneDrive again.

Fix 3: Delete corrupted library files

Sometimes the cache files that help OneDrive run fast become corrupted. Deleting them forces the application to build fresh ones.

1. Click on your desktop so Finder is the active program.
2. Click Go in the top menu bar, hold down the Option key, and click Library.
3. Open the Containers folder. Find and delete the folder named com.microsoft.OneDrive.mac.
4. Go back to the main Library folder and open Application Support. Delete the OneDrive folder.
5. Go back to the main Library folder and open Caches. Delete the folder named com.microsoft.OneDrive.
6. Restart your Mac and launch the application.

Fix 4: Reset the OneDrive application

If the app is still broken, you can run a hidden script packed inside the application to factory reset its internal settings.

1. Open your Applications folder.
2. Right click or Control click on the OneDrive app and choose Show Package Contents.
3. Open the Contents folder, then open the Resources folder.
4. Look for a file named ResetOneDriveApp.command or ResetOneDriveAppStandalone.command.
5. Double click this file. A Terminal window will open and run a few scripts.
6. Once the terminal says the process is complete, close the window and open OneDrive.