I just had a thought. The servers that are working are running under the default port #, the others that I'm having issues with are not. I tried to connect to a problem server with the port included in Management Studio to make sure I get the string correct before adding to the ServerList table. The string that worked was ServerName.domain.com,Port#\Instance. I added this to the table, but it still errors out! Am I doing something wrong? I feel like this is the smoking gun!