When an instance is upgraded from Helsinki to Istanbul, there is a possibility that a workflow requiring the use of a MID Server will fail. This can occur when the user runs the workflow manually or when it is triggered by a business rule. The resulting error message states: "Fault description: Unable to find any application matchable to the requested Application: Orchestration."
This error occurs when the instance has been upgraded to Istanbul code, but the database is still in the process of upgrading. Orchestration attempts to select the MID Server, which relies on an updated database that is not available yet. No MID Server can be selected, and the workflow fails.
Wait until the upgrade is complete before running any workflows that require the MID Server.