OneDrive is unable to access keychain

I had this same problem a couple of days ago. The solution that worked for me was to delete the OneDrive Cached Credential key from the Keychain. The procedure was the following:

1. Launch Spotlight Search (shortcut: command + space), type keychain, and press return. This should launch the Keychain Access app.
2. Type OneDrive into the Keychain Access search box. This should show a short list of keys related to OneDrive.
3. Click on the key called "OneDrive Standalone Cached Credential" or some variant thereof.
4. Press the delete key (or use the menu item Edit > Delete) to delete the cached credential key.

Cross your fingers (optional 🙂) and start up OneDrive again. If all goes well, it will now work properly. They system will automatically re-create the deleted key.

Good luck!