Software⏱️ 3 min read📅 2026-06-19

How to Fix Error 26 Error – Connect to SQL Server. Error 26 : the type initializer threw an exception: error locating server instance specified

SQL Server connection issue with Error 26: error locating server instance specified.

Quick Answer: Verify that the SQL Server instance name is correct and try using the fully qualified domain name (FQDN) of the server.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🛠️ Step-by-Step Verified Fixes
  3. 💡 Conclusion

Error 26: 'the type initializer threw an exception: error locating server instance specified' occurs when attempting to connect to a SQL Server instance from a remote machine. This issue primarily affects users who need to access their SQL Server databases from outside the local network.

This problem is frustrating because it can be challenging to diagnose, especially when the issue arises from a seemingly working setup. However, with the right troubleshooting steps, you should be able to resolve this issue and connect to your SQL Server database successfully.

🔍 Why This Happens

  • The primary reason for Error 26 is that the SQL Server instance name or IP address specified in the connection string does not match the actual server instance name or IP address. This could be due to a misconfiguration, incorrect network settings, or a change in the server instance's configuration.
  • An alternative cause could be related to the firewall rules or network restrictions on the client machine that are blocking the SQL Server connection.

🛠️ Step-by-Step Verified Fixes

Configuring the SQL Server Instance Name

  1. Step 1: Step 1: Determine the correct instance name of your SQL Server Express installation. This can be found in the SQL Server Management Studio (SSMS) or by querying the 'sp_hadlog' stored procedure on the server.
  2. Step 2: Step 2: Update the connection string with the correct instance name. For example, if your server IP address is 192.168.0.1 and your instance name is 'SQLEXPRESS', update your connection string to `server=192.168.0.1\SQLEXPRESS;`.
  3. Step 3: Step 3: Restart your application or the SQL Server service to apply the changes.

Configuring Firewall Rules

  1. Step 1: Step 1: Check if any firewall rules are blocking the connection to your SQL Server instance. You can do this by querying the Windows Firewall with Advanced Security (WFAS) or using a tool like Netsh.
  2. Step 2: Step 2: If necessary, create a new rule or modify an existing one to allow incoming connections on TCP port 1433 and UDP port 1434 to your SQL Server instance. Make sure to include any required authentication settings.

💡 Conclusion

To resolve Error 26, you should first verify the correct instance name of your SQL Server Express installation and update your connection string accordingly. If the issue persists, check your firewall rules and configure them to allow incoming connections to your SQL Server instance. By following these steps, you should be able to connect to your SQL Server database successfully from a remote machine.

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