tI'd check for three things:
1. Make sure the SQL Broswer service is running. That is the Service that handles the part of the connection when you request machinename\Instance1 , it tells the service which dynamic port that service is using (ie 1711).Remember the Express by default will be using dynamic ports.
2. Next, Express, by default, does not allow remote connections...you have to explicitly enable it.
3. Windows Firewall will prevent connections unless you tel it otherwise. after you make sure of the two steps above, turn off windows firewall, and tryu to connect froma remote machine. If you can connect, then you know you need to change windows fireall to allow the three express instances to connect.
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