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