Power BI external guest user receiving login.live.com page error

We are testing granting external guest users access to our Power BI reports.  We have issued an invite to an external guest user with a Microsoft account and have granted their account rights to one of our internal Power BI Pro licenses.  We are federated with Microsoft.  The external guest user received the e-mail invite with the link to the report.  The first time they tried it, our ccompany authentication page sent them to Microsoft for authentication and then they were able to access the report.  Everytime since when they supply their credentials on our company authentication page they receive a "This login.live.com page can't be found" error.  They have tried using both Edge and Chrome and have also cleared caches etc.  In the details of the error message it says: "No webpage was found for the web address:  https://login.live.com/oauth20_authorize.srf?"