Named Pipes Provider, Error: 40 - Could not open connection to SQL Server

Has anyone encountered this error?

I added TCP port 1433 to the inbound firewall rules, and I also made sure that named pipes are enabled. But still, I cannot connect to SQL Server (2008 R2).

I appreciate any suggestions. Thank!

A network or specific instance error occurred while creating a connection to SQL Server. The server was not found or was unavailable. Verify that the instance name is correct and that SQL Server is configured for a remote connection. (provider: Named pipes Provider, error: 40 - Could not open connection to SQL Server) (Microsoft SQL Server, error: 2)