Most of you must have faced this error and a lot of times it is resolved by restarting SQL agent services or by enabling named pipes in SQL Service Configuration Manager. But this time i discovered something new. For your information, i had my database and application on different servers. In order to resolve this i had to add port 1434 (UDP Protocol Type) in Windows Firewall Inbound Rules. 

Open Windows Firewall Advanced Security, and from there navigate to Inbound Rules>>New Rule.

Navigate to Protocols and Ports, select UDP in Protocol Type and add port 1434, 

That is it ! :)