7 things to check to resolve “A network-related or instance-specific error occurred while establishing a connection to SQL Server…” by Donabel Santos, edited by Moojjoo

If you get the following 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) ”

Things to check:

1. Make sure your database engine is configured to accept remote connections

2. Check the SQL Server service account

• If you are not using a domain account as a service account (for example if you are using NETWORK SERVICE), you may want to switch this first before proceeding

3. If you are using a named SQL Server instance, make sure you are using that instance name in your connection strings in your ASweb P.NET application

• Usually the format needed to specify the database server is machinename\instancename
• Check your connection string as well

<connectionStrings>

<add name="SampleConnectionString" connectionString="Data Source=machinename\instancename;Initial Catalog=AdventureWorks;Integrated Security=SSPI;Min Pool Size=5;Max Pool Size=60;Connect Timeout=30″ providerName="System.Data.SqlClient"/>

</connectionStrings>

4. You may need to create an exception on the firewall for the SQL Server instance and port you are using

• Start > Run > Firewall.cpl
• Click on exceptions tab
• Add the sqlservr.exe (typically located in C:\Program Files (x86)\Microsoft SQL Server\MSSQL.x\MSSQL\Binn, check your installs for the actual folder path), and port (default is 1433)
• Check your connection string as well

5. If you are using a named SQL Server instance, make sure you are using that instance name in your connection strings

6. Check SQLBrowser; check that it is running. You may also need to create an exception in your firewall for SQLBrowser.

7. Check that you have connectivity to the SQL Server. 

Note what you are using to connect: machine name, domain name or IP address? Use this when checking connectivity. For example if you are using myserver
• Start > Run > cmd
•netstat -ano  right click on the window title and use find 1433
•telnet myserver 1433
•ping -a myserver

Check what ports are IP addresses are being returned.

If you still can’t get any connection, you may want to create a SQL account on the server, a corresponding SQL user on the database in question, and just use this username/password combo in your web application.