Hi @James Robbins ,
Welcome to our forum!
According to my search, this issue occurs because of the presence of duplicate tokens in the keychain.
To work around this issue, delete any cached passwords for your account, and also delete any modern authentication tokens from the keychain.
- Quit Outlook and all other Office applications.
- Start Keychain Access by using one of the following methods:
- Select the Finder application, click Utilities on the Go menu, and then double-click Keychain Access.
- In Spotlight Search, type Keychain Access, and then double-click Keychain Access in the search results.
- In the search field in Keychain Access, enter Exchange.
- In the search results, select each item to view the Account that's listed at the top, and then press Delete. Repeat this step to delete all items for your Exchange account.
- In the search field, enter adal.
- Select all items whose type is MicrosoftOffice15_2_Data:ADAL:<GUID>, and then press Delete.
- In the search field, enter office.
- Select the items that are named Microsoft Office Identities Cache 2 and Microsoft Office Identities Settings 2, and then press Delete.
- Quit Keychain Access.
Hope this can help you!
If the answer is helpful, please click "Accept Answer" and kindly upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.