1. Server Not Running

• Ensure that the SQL Server instance you are trying to connect to is running. You can check this using the SQL Server Configuration Manager. If the instance is stopped, right-click and select Start.

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2. Incorrect Connection Settings

• Verify that you are using the correct server name and instance name in your connection string. For named instances, the format should be ServerName\InstanceName. If you are using the default instance, you can simply use localhost or the server's IP address.

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3. Firewall Issues

• Windows Firewall or other network firewalls may block the connection to SQL Server. Ensure that the firewall allows traffic on the SQL Server port (default is 1433). You may need to add an inbound rule to allow SQL Server through the firewall.

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4. TCP/IP Protocol Disabled

• Check if the TCP/IP protocol is enabled for your SQL Server instance. This can be done in the SQL Server Configuration Manager under SQL Server Network Configuration. If it is disabled, enable it and restart the SQL Server service.

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5. Authentication Issues

• Ensure that you are using the correct authentication method. SQL Server can be configured to use either Windows Authentication or SQL Server Authentication. Make sure your connection settings match the authentication mode configured on the server.

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6. Certificate Trust Issues

• If you encounter errors related to certificate trust, such as "The certificate chain was issued by an untrusted authority," you may need to check the connection security settings in SSMS. You can enable the option to trust the server certificate in the connection dialog.

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  By addressing these common issues, you should be able to resolve most connection errors encountered in SQL Server Management Studio. If problems persist, consider checking the SQL Server logs for more detailed error messages or consulting the official documentation for further troubleshooting steps.
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