Encryption keys for multiple report server instances were detected
Upgrade Advisor has detected encryption keys for multiple report server instances, indicating that the current report server is part of a scale-out deployment. All servers in the scale-out deployment must run the same version of Reporting Services. If you are upgrading a report server instance that is part of a scale-out deployment, the other report server instances will be unavailable until you upgrade them to the same version.
A scale-out deployment consists of two or more report servers that share a single report server database. Upgrade Advisor checks for scale-out deployments by scanning for database encryption keys that are owned by different report server instances.
If you upgrade one report server instance that is part of a scale-out deployment, you must upgrade all of the other report server instances in the scale-out deployment to the same version. Otherwise, users who attempt to connect to those report server instances will receive a database incompatibility error message.
Note that this warning will also occur for single server deployments if you moved a report server database from one computer to another. In this scenario, the report server database will contain multiple keys for the previous and current installation, where the keys from the previous installation exist but are ignored. If the report server is not part of a scale-out deployment, you can continue with upgrading the single report server and ignore the warning about multiple encryption keys. Unused keys in the report server database will not affect upgrade or report server operations. You can use the Reporting Services Configuration tool to view the report servers that have encryption keys in the report server database.