Why did a network-related or instance-specific error occur while establishing a connection to SQL Server?

Your connection string was probably overriden when you copied your new website version on the server. Please check the connection string in web.config and see if it is valid.

If you are connecting from Windows Machine A to Windows Machine B (server with SQL Server installed) and are getting this error, you need to do the following:

On Machine B:

Turn on the Windows service called "SQL Server Browser" and start the service In Windows Firewall: enable incoming port UDP 1434 (in case SQL Server Management Studio on machine A is connecting or a program on machine A is connecting) enable incoming port TCP 1433 (in case there is a telnet connection) In SQL Server Configuration Manager: enable TCP/IP protocol for port 1433

I've resolved the issue. It was due to the SQL browser service.

Solution to such problem is one among below -

Check the spelling of the SQL Server instance name that is specified in the connection string.

Use the SQL Server Surface Area Configuration tool to enable SQL Server to accept remote connections over the TCP or named pipes protocols. For more information about the SQL Server Surface Area Configuration Tool, see Surface Area Configuration for Services and Connections.

Make sure that you have configured the firewall on the server instance of SQL Server to open ports for SQL Server and the SQL Server Browser port (UDP 1434).

Make sure that the SQL Server Browser service is started on the server.

link - http://www.microsoft.com/products/ee/transform.aspx?ProdName=Microsoft+SQL+Server&EvtSrc=MSSQLServer&EvtID=-1

check forthe followings :

Make sure your database engine is configured to accept remote connections

• Start > All Programs > SQL Server 2005 > Configuration Tools > SQL Server Surface Area Configuration • Click on Surface Area Configuration for Services and Connections • Select the instance that is having a problem > Database Engine > Remote Connections • Enable local and remote connections • Restart instance

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

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

the cause is that SQL SERVER is stopped from services.msc a solution for this problem could be starting SQL SERVER from services.msc

https://i.stack.imgur.com/2xbHt.png

I had the same problem with SQL Server 2008 R2 and when I checked "SQL Server Configuration Manager" My SQL Server instance had Stopped. Right Clicking and Starting the Instance solved the issue.

we have to enable TCP/IP property in sql server configuration manager

I recently had this problem and it ended up being a port issue. My production SQL Server was set up at to be port 1427 instead 1433.

Just change the connection string to be

...data source=MySQLServerName,1427;initial catalog=MyDBName...

Hope this helps anyone who might be seeing this same issue.

If your server was working and suddenly started erroring out, your server/instance stopped and connection settings were changed somehow.

For SQL Server 2008 here is how you can fit this:

Goto Start > All Programs > SQL Server 2008 > Configuration Tools > SQL Server Configuration Manager > SQL Server Services. And here you'll see all the instances and their state. The state of the instance you were trying to connect can be stopped here. Double click on the instance and then click on connect. It will connect and now go back and run your application, you will be able to connect with no error.

This solution assumes the error is not being caused by something wrong in your connection string.

In my case it was a very silly error. I was using a library to read the connection string out of a config file, and I forgot to double back slash.

For example I had: localhost\sqlexpress which was read as localhostsqlexpress when I should rather have had localhost\\sqlexpress note the \

I had same problem regarding that i.e A network-related or instance-specific error occurred while establishing a connection to SQL Server.

I was using SQL Server 2005 (.\sqlexpress)` and worked fine but suddenly services stopped and gave me error.

I solved it like this,

Start -> Search Box - > Sql Configuration Manager -> SQL Server 2005 Services >and just Change Your SQL Server (SQLEXPRESS) State to Running by right clicking that service Sate.

I solved this issue by running the following command in an elevated command prompt as specified in this post.

net start mssqlserver

I had the same problem but found that it was because the password for my Service Account for the Database Engine had expired. The solution was to login to that account, fix this, then set the account so password never expires.

My remote sql server was expecting connection at a different port and not on the default 1443.

The solution was to add a "," after your sql server IP and then add your port like so 129.0.0.1,2995 (Check the " , " after server IP)

Please find the image for reference below.

https://i.stack.imgur.com/k88MP.png

I had the same error, and it turned out .NET created a database on localhost which I wasn't aware of. When I tried to get the site live it didn't create the database, so the code was pointing to a database that was non existent.

Hopefully this might help some other people out trying to troubleshoot.