If you have not, try setting the default value for the SVR_Conn variable to (local) or to your server name \ instance name . That worked for me.
I also set the default server name to use the instance name where I created the SQL_Overview database. I did this for all of the connections. My default instance is not running so the connections fail. However, since the MultiServer connection has an expression, that required setting the variable to a valid server.