This is something that has happened to me both in Mac and in Windows versions of MS Office. I try to open a file and then dialog boxes show an authentication process in progress, but the authentication process eventually fails after several repetitions.

In both cases, this is caused by corrupt login credentials stored in your operating system. In Windows, these credentials are held in the Windows Credential Manager. In Mac OS, these credentials are held in the Keychain Access app.

The cure for this is to simply delete your old credentials. As a best practice, I usually delete every credential that relates to Microsoft, Office, or any of the related services, such as Exchange, OneDrive, etc.

The Windows Credential Manager is found by going to All Control Panel Items > Credential Manager. The Keychain Access app is within the Applications section; go to Finder > Applications > Utilities > KeyChain Access.

Of course, the caveat here is that you are now going to have to log in to your applications as if for the first time, so you must be prepared with proper passwords and perhaps other means of authentication, like app passwords or multifactor authentication prompts.

Maladies such as this are a fact of life – corruption happens.

Now if this were a corruption of a file itself, then what? If it happened recently, then you can always go to OneDrive online and find a previous version to restore. But if you need to restore a corrupt file to a good-working version over a month old or after 500 versions, then I hope you have a backup system in place. That said, you *can* set your data to be governed by a retention policy and thereby held without deletion indefinitely, however, finding and restoring such data can be daunting. This is why we include cloud backup with single-click restore as part of an all-inclusive bundle of products and services when quoting an IT management arrangement for your company.