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

Well i have a big problem that i'm trying for days to solve but i could not do it, so i need your help. I have a web application in asp.net 4.0 where i implemented custom membership and role providers. When i open the app homepage in it connects to the database and retrieves some information. There is also a login form and when i login it validates the user through the database and redirects me to the reserved pages but than this error appears:

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)

Description:

An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details:

System.Data.SqlClient.SqlException: 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)

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

I tried many things, some solution i found in stackoverflow but nothing worked. Here are my connectionstrings:

<connectionStrings>
  <clear/>
  <remove name="LocalSqlServer"/>
     <add name="LocalSqlServer" connectionString="Data Source=MSSQL2008-1;Initial Catalog=agency;
        Integrated Security=False;User ID=adis_agency;Password=niarda2012;Connect Timeout=180;Encrypt=False;
        Packet Size=4096" providerName="System.Data.SqlClient" />
     <add name="AgencyConn" connectionString="Data Source=MSSQL2008-1;Initial Catalog=agency;
        Integrated Security=False;User ID=adis_agency;Password=niarda2012;Connect Timeout=180;Encrypt=False;
        Packet Size=4096" providerName="System.Data.SqlClient"/>
</connectionStrings>

Below are also the membership and role manager web.config section:

<membership defaultProvider="AuthProvider">
  <providers>
    <clear/>
      <add name="AuthProvider" type="AuthenticationProvider" applicationName="~/Reserved/" connectionStringName="AgencyConn"/>
  </providers>
</membership>
<roleManager enabled="true" defaultProvider="MyRoleProvider">
  <providers>
    <clear/>
      <add name="MyRoleProvider" type="RoleAccessProvider" connectionStringName="AgencyConn"/>
  </providers>
</roleManager>

Please can anybody help to figure out whats wrong?

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:

1.) turn on the Windows service called "SQL Server Browser" and start the service

2.) in the 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)

3.) in the Windows firewall, enable incoming port TCP 1433 (in case there is a telnet connection)

4.) in SQL Server Configuration Manager, enable TCP/IP protocol for port 1433

For me the issue was that the DNS record was wrong...

The following, which proved very helpful, is largely taken from this blog post.

This error message is actually pretty specific and the solution quite simple.

You get this error message only if you are trying to connect to a SQL Server named instance. For a default instance, you never see this because even if we failed at this stage (i.e. error locating server/instance specified), we will continue to try connect using default values, e.g default TCP port 1433, default pipe name for Named Pipes.

Every time a client makes a connection to SQL Server named instance, we will send a SSRP UDP packet to the server machine UDP port 1434. We need this step to know configuration information of the SQL instance, e.g., protocols enabled, TCP port, pipe name etc. Without this information the client does not know how to connect and it fails with this error message.

In a word, the reason that we get this error message is the client stack could not receive SSRP response UDP packet from SQL Browser. In order to isolate the exact issue follow these steps:

Make sure your server name is correct, e.g., no typo on the name.
Make sure your instance name is correct and there is actually such an instance on your target machine. (Be aware that some applications convert \ to ).
Make sure the server machine is reachable, e.g, DNS can be resolve correctly, you are able to ping the server (not always true).
Make sure the SQL Browser service is running on the server.
If the firewall is enabled on the server, you need to put sqlbrowser.exe and/or UDP port 1434 into exception.

There is one corner case where you may still fail after you checked steps 1 to 4. It also may happen when:

your server is a named instance on cluster or on a multi-homed machine
your client is a Vista machine with Firewall on.

A tool which could prove useful (it did for me) is PortQry. If this command returns information and it contains your target instance, then you can rule out possiblity 4) and 5) above, meaning you do have a SQL Browser running and your firewall does not block SQL Browser UDP packet. In this case, you can check other possible issues such as an incorrect connection string.

As a final note, the error message for the same issue when you use SNAC is: [SQL Native Client]SQL Network Interfaces: Error Locating Server/Instance Specified [xFFFFFFFF].

Microsoft recently released a guided walk through that can serve as a one stop shop to troubleshoot a majority of connectivity issues to SQL Server: Solving Connectivity errors to SQL Server

The answer is in the error message itself:

Error Locating Server/Instance Specified

Basically, you've got the wrong server\instance in the connection string, i.e. this bit:

Data Source=MSSQL2008-1

is wrong and not pointing to the server, or the servername doesn't resolve to an IP address. Two other posibilities: (1) the SQL Browser Service on the box running SQL Server isn't running or (2) Windows Firewall (or some other firewall) on the SQL box is denying incoming connections.

Ultimately, if the servername is correct, then it turns into a networking problem, and you need to find out why the client cannot connect to the server (and this will be more likely to be a basic networking problem than a SQL Server configuration problem).

Kristian Nissen

I had been experiencing the same problem, in my ASP.NET MVC 4 application.

The way I solved it, was in the DatabaseContext. By passing down the name of the connection string I wanted to use through the base constructor.

public class DatabaseContext : DbContext
{ 
    public DatabaseContext()
        : base("DefaultConnection") // <-- this is what i added.
    {
    }

    public DbSet<SomeModel> SomeModels { get; set; }
}

Goto window+R and type services.msc and press enter.

Then start SQL server manually if not automatically started.

Then you try to login, it must be works.

I had the same error and I started the SQL Server Express service and it worked. Hope this helps.

Change your .\SQLEXPRESS,and add your SQL express name only and it works for me

 <add name="BlogDbContext" connectionString="data source=your name here; initial catalog=CodeFirstDemo; integrated security=True" providerName="System.Data.SqlClient"/>

We got the same issue recently. We found out that the code is looking for the connection string named "LocalSqlServer" in the machine.confg file. We added this line and it is working fine.

i had this issue, and fixed it. the problem seemed to be this:

wrong:

<add key="aaa" value="server=[abc\SQL2K8];database=bbb;uid=ccc;password=ddd;" />

right

<add key="aaa" value="server=abc\SQL2K8;database=bbb;uid=ccc;password=ddd;" />

The issue is caused by the DNS failing to resolve the hostname. Try using the IP address instead of the "computer name".

In my instance, the name of the connectionString in the web.config file was spelled wrong. This is the name of the database context Entity Framework uses. I guess this is the error you get when EF can't match up the connectionString name with the context.

In my case I searched for services. Then found a service called "SQL Server(SQLEXPRESS). Then right click on that. Select properties. Then click start. That's all. Solved the issue.

This problem took me about one day, on one of mine ASP.NET MVC project fortunately i had the problem on my machine and not in production environment, so comparing web.config i see and removing that the error disappeared... a true challenge connect the SQL Server error 26 to this problem

Same issue. In my case I solved setting the project as the "StartUp Project".

来源：https://stackoverflow.com/questions/13754563/sql-network-interfaces-error-26-error-locating-server-instance-specified

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ASP.NET

sql-server-2008

asp.net-membership

membership-provider

roleprovider