You may have noticed that version 5.8 no longer accepts local server credentials to be used to manage the PMAdmin site. Even when added to the local admin and PMAdmin groups. The error “Authentication failed” is produced when login is attempted.
This is by design. Due to changes introduced to version 5.8.1, local credentials can no longer be used to manage the PMAdmin site. An enhancement request (VSTS97255) has been created detailing the feature.
The product team will evaluate the request and this feature may become available on a future release of the product.
Please refer to this article for updates or contact support referencing the Enhancement Request ID: VSTS97255.