When trying to logon to Enterprise Reporter Report Manager using Windows/Integrated Authentication you receive the same or similar error as the following:
The cause of the error has been determined to be a Kerberos related issue. The SQL Server requires a Service Principal Name (SPN) in order to allow other services to authenticate again SQL services using Kerberos (also applies to other services). This SPN has not been registered for some reason.
The Service Principal Name (SPN) needs to be added to the SQL Server Active Directory Computer account. Please speak to your DB Administrator and AD Administrator to verify and correct the SPN requirements.
A possible workaround to adding the SPN would be to permission the account or a group to the ER database:
If you are not sure weather you are affected by this issue you can verify/confirm by collecting a network trace while reproducing the logon using Report Manager.
Wireshark or MicNetwork Monitor are common tools to trace network communication. Using either of these tools you would see the same or similar error as follows:
error-code: eRR-S-PRINCIPAL-UNKNOWN (7)
Troubleshooting Kerberos Authentication