error: 40 - Could not open a connection to SQL Server

Dear,

I read the following pages and do all that is written:

https://www.mssqltips.com/sqlservertip/2340/resolving-could-not-open-a-connection-to-sql-server-errors/

http://blog.sqlauthority.com/2009/05/21/sql-server-fix-error-provider-named-pipes-provider-error-40-could-not-open-a-connection-to-sql-server-microsoft-sql-server-error/

http://blogs.msdn.com/b/sql_protocols/archive/2007/03/31/named-pipes-provider-error-40-could-not-open-a-connection-to-sql-server.aspx

http://blogs.technet.com/b/mdegre/archive/2011/06/04/resolve-sql-server-connectivity-issues.aspx

http://social.technet.microsoft.com/wiki/contents/articles/2102.how-to-troubleshoot-connecting-to-the-sql-server-database-engine.aspx

Although it was all done properly and still comes error:

One or more errors occurred. A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: Named Pipes Provider, error: 40 - Could not open a connection to SQL Server)

DataSource: IP_ADDRESS, PORT
Database: NAME_DB

The server on which the application requires connecting to the SQL server. Mistakes come every hour.
How to finally remove the mistake? Do you have any idea?