A connection was successfully established with the server, but then an error occurred during the login process. (Error Number: 233)

Solution 1:

For SQL2008,

• open Management Studio
• Rt click on instance
• go to properties
• select Security
• Under Server Authentication, check SQL Server and Windows Authentication Mode
• hit OK

Restart the server using configuration manager.

Solution 2:

Turn out to be some SQL service was stopped somehow on server. Restarting SQL Server service manually was the solution.

Solution 3:

the following points work for me. Try:

1. start SSMS as administrator
2. make sure SQL services are running. Change startup type to 'Automatic'

3. In SSMS, in service instance property table, enable below: