When you try to upgrade to Virtual Machine Manager 2016, the attempt may fail if the VMM database is using a Microsoft SQL Server database that leverages the AlwaysOn Availability Groups feature. In this situation, the following error is returned:
10:16:43:InnerException.Type: System.Data.SqlClient.SqlException, InnerException.Message: The operation cannot be performed on database "VirtualManagerDB" because it is involved in a database mirroring session or an availability group. Some operations are not allowed on a database that is participating in a database mirroring session or in an availability group.