The event can take place after a member server is promoted to Domain Controller, and reporting services were installed on it before promotion and were configured to use the NETWORK SERVICE (or another built-in one) account to connect to the SQL server on the same host.
Use rsconfig util (i.e. rsconfig -c -a windows) to recreate valid encrypted connection information.
From a newsgroup post: "Check the ReportServer service. See what dependencies it has. Perhaps it should be configured to start only after the SQL Server services have started, so that the ReportServer service finds the SQL Server to attach to. However, this is not desirable if the SQL server is not on the same box. If the service cannot talk to the SQL catalog, it will continue to try until it is successful. Therefore, even if the ReportServer service starts first, once SQL server starts, everything should start to work".