Cannot connect to a SQL Server 2014 Express database intermittently I have problems connecting computers running Windows 7 to a database SQL Server 2014 Express intermittently.

It happens that, intermittently, I can not connect to the database that is on a Windows 2008 R2 server.

If I restart the computer, works again, but only for a few minutes, sometimes hours.

The Firewall of my computer is turned off. Windows Firewall is turned off.

CONFIGURATION:


The server is Windows Server 2008 R2 Foundation
Firewall Ports TCP / IP and UDP 1434 1433 allowed


SQL Server Express:


Unlimited Connections
Allows remote connections
Timeout remotely query: 600 seconds


Machines with Windows XP have no problem with this issue.
Finally, it seems to have turned the problem: an IP in the secondary DNS configuration caused the problem.
Removing the IP, everything works correctly again.