Added an instance which is a publisher, ( and also acting as the distributor). getting this error:
you would need to update Client Tools to ver.10 (SQL Server 2008) since SQL Server won’t allow downgrade.
Then run Windows Explorer (on the DiagnosticServer machine), navigate to the C:\WINDOWS\assembly and verify versions of Microsoft.SqlServer.ConnectionInfo, Microsoft.SqlServer.Rmo and other assemblies are the same.
Then restart QDS service (under control panel)