Login failed- The user is not associated with a trusted SQL Server connection

 The Error number 18452 is similar to this issue.

The message "Login failed. The user is not associated with a trusted SQL Server connection" usually indicates that the connection attempt is being made with Windows Authentication, but the user is not recognized or trusted by the SQL Server.

Here are some steps to resolve this issue:

1. Check Authentication Mode

Ensure that the SQL Server is set to allow Windows Authentication (or Mixed Mode if you need both Windows and SQL Server authentication):

1. Open SQL Server Management Studio (SSMS).
2. Connect to the SQL Server instance.
3. Right-click the server in Object Explorer and select "Properties."
4. Go to the "Security" page.
5. Ensure "SQL Server and Windows Authentication mode" is selected.
6. Click "OK" and restart the SQL Server service if you made any changes.

2. Verify User Permissions

Ensure that the Windows user or group attempting to connect has the necessary permissions on the SQL Server:

1. In SSMS, navigate to Security > Logins.
2. Right-click and select "New Login" if the user doesn't already exist.
3. If the user exists, right-click the user and select "Properties."
4. Ensure the login is mapped to the appropriate database(s) and has the necessary roles and permissions.

3. Network and Domain Configuration

Ensure that the client machine and the SQL Server are in trusted domains or that the client machine is correctly joined to the domain:

1. Ensure the client machine is properly joined to the domain.
2. Verify that the domain of the client machine is trusted by the domain of the SQL Server.
3. Check the domain controller and Active Directory settings to ensure proper trust relationships are established.

4. Service Principal Names (SPNs) for Kerberos Authentication

If you are using Kerberos authentication, ensure that SPNs are properly configured for the SQL Server service account:

1. Use the setspn command to check and register SPNs. For example:

setspn -L <domain\username>
setspn -A MSSQLSvc/<hostname>:1433 <domain\username>
setspn -A MSSQLSvc/<hostname>.<domain>:1433 <domain\username>

5. Check Local Security Policies

Ensure that the local security policies on the client machine allow for delegation and trust the SQL Server:

1. Open the Local Security Policy management console (secpol.msc).
2. Navigate to Local Policies > User Rights Assignment.
3. Ensure "Access this computer from the network" includes the user or group.
4. Ensure "Deny access to this computer from the network" does not include the user or group.

6. Check SQL Server Configuration

Ensure that the SQL Server is configured to accept connections from the specific domain:

1. Open SQL Server Configuration Manager.
2. Go to SQL Server Network Configuration > Protocols for [Your Instance].
3. Ensure TCP/IP is enabled.
4. Check the IP addresses and ensure they are configured correctly.

Example Connection String for SQL Server Authentication

If switching to SQL Server Authentication, you can use the following connection string format:

string connectionString = "Server=myServerAddress;Database=myDataBase;User Id=myUsername;Password=myPassword;";

Conclusion

If these steps do not resolve the issue, it may be necessary to work with your network or domain administrator to ensure all settings are correctly configured and that there are no underlying network or domain issues.