While connecting to SQL Server, users may sometimes encounter the following error: “A network-related or instance-specific error occurred while establishing a connection to SQL Server...” This issue usually happens due to incorrect server details, SQL Server service issues, network problems, or permission-related errors. In this article, we will look at common SQL Server connection errors and their possible solutions. Error 1: A Network-Related or Instance-Specific Error Occurred Error Message: “A network-related or instance-specific error occurred while establishing a connection to SQL Server...” Possible Reasons: 1. Incorrect Server Name Make sure the SQL Server name or instance name entered in the connection string or SSMS is correct. 2. SQL Server Service Not Running The SQL Server Database Engine service may not be in the RUNNING state. Solution Open SQL Server Configuration Manager or Services Check the status of: SQL Server SQL Server Browser Start the services if they are stopped 3. Network Connectivity Issues There may be a network-related issue between the client machine and the SQL Server. Solution Verify network connectivity Ping the server Check firewall settings Ensure the SQL Server port is open Error 2: Login Failed for User Error Message “Login failed for user 'peter'. (Framework Microsoft SqlClient Data Provider). Error Number: 18456” Reason This error generally occurs due to insufficient permissions or invalid login credentials. Solution Contact the Database Administrator (DBA) and ensure: The user account has proper access permissions SQL authentication is enabled (if required) The login is mapped to the required database Error 3: SSL Certificate Trust Issue Error Message: “A connection was successfully established with the server, but then an error occurred during the login process. (provider: SSL Provider, error: 0 - The certificate chain was issued by an authority that is not trusted.) (Framework Microsoft SqlClient Data Provider)” Reason: This issue occurs because the SSL certificate used by SQL Server is not trusted by the client machine. Solution: You can temporarily disable encrypted connections in SQL Server Management Studio (SSMS). Steps to Fix Open SQL Server Management Studio (SSMS) In the login window, click Options Go to the Connection Properties tab Uncheck the option: Encrypt Connection Click Connect