Power BI report server upgrade cannot maintain old reports

[MGoo]

We upgraded our Power BI Report Server from the June 2017 release to the new March 2018 release, also upgraded the Power BI desktop on local machine.

Reports created by June 2017 verison of PBI and saved to the reporting server are still working

Reports created by March 2018 version of PBI  and saved to the reporting server are working

Reports originally created by June 2017 version and updated by March 2018 version are displaying the error  "We couldn't connect to the Analysis Services server. The server forcibly closed the connection. To connect as the user viewing the report, your organization must have configured Kerberos constrained delegation."

Even saved the report with a new name but made no difference.

[Jon-Heide · Accepted solution]

There may be cases, especially if there are cached models in reports, where reuploading the reports may be required after an upgrade. Also, do try resetting the user account credentials for the reports under the data source managment page. 

[MGoo]

Many thanks. It ws to do with the user credentials.