If Information Reference System was installed in Client-Server mode, i.e. database was installed on the server and client applications were installed on different PCs, it is required to perform additional database server setup to enable access to the database. It is mandatory even if MS SQL Server was installed automatically during Information Reference System installation.
TCP/IP protocol is disabled by default but required to be active. To enable it run SQL Server Configuration Manager from Windows "Start" menu (All Programs\Microsoft SQL Server 2012\Configuration Tools).
Expand SQL Server Network Configuration tree node in the left panel, then select your SQL Express instance (REGULA in our example). Open TCP/IP option and change parameter Enabled from No to Yes.
To changes take effect you should restart MS SQL Server. It can be done during operating system restart but you can do it manually from SQL Server Configuration Manager. Select SQL Server Services tree node in the left panel, then SQL Server. Click the button Restart Service.
Wait until the service is restarted.