Recently I had the need to migrate the SSRS web portal / services for an existing installation to a new server. I followed the steps I had used previously, which included:

1. Backing up and restoring the encryption key (see this)
2. Adding the new server’s computer account to the RSExec role in the msdb, ReportServer, and ReportServerTempDB databases

However, when browsing the SSRS web page, I got an error message. Upon looking in the log files, I found the following message. I assumed this was because there was another instance of Reporting Services running, namely that on the original server. Since SQL Server Standard edition doesn’t allow more than one server (a.k.a Scale Out Deployment), it seemed appropriate that this no longer worked. After stopping the services on the old machine, the error persisted, however. After researching some more, I ran the following query against the report server database to remove the record of the old server. Once that was completed, the SSRS web page loaded without further issue.