A network-related or instance-specific error occurred while establishing a connection to SQL Server.

Error: 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: SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified)

Solution:

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/

1. The issue may be due to firewall.
2. SQL browser service is not running
3. SQL Server is not configured to allow remote connection
4. Check whether tcp/ip protocol is enabled for communication in sql server configuration manager -> Client and server protocols
5. Check tcp/ip protocols are enabled and active.
6. check whether you sql server logins are properly created and provided necessary level of authentication.

Cheers,
Venkatesan Prabu .J
Head, KaaShiv Infotech