Enable Remote access on #SQL server named instance
You can install two instances of SQL server on the same machine, for example if you really needed to have two different versions of SQL server, or wanted to create a logically separated database where you could keep a near-identical copy of your main database.
Anyway, for whatever reason, if you do install two instances of SQL server on one server, you will quickly find that the default port number 1433 is occupied by the first SQL server, for local connections this doesn’t cause a problem, but for remote connections it does.
First, you have to pick a new port for the named instance. Open SQL server configuration manager, then select SQL Server Network Configuration, then SQLExpress (Or whatever you named your second instance), select TCP/IP, enable it, if it isn’t already. Then right click properties. Select the IP Addresses tab, and scroll to the IP (ALL) heading, remove the 0 from TCP Dynamic ports, and enter a number such as 1444 into the TCP port box. Open up services, and restart the service associated with the SQLExpress instance.
You may now need to open up TCP port 1444 on your firewall, and adjust your connection strings to <IP Address>\<Instance Name>,1444
Network Programming in .NET 