thanks for the reply! I've checked the instance name is correct and the firewall is ok. The app has been running successfully for 6 months. I've actually found the reason for the failure. The account is a domain account and the password was accidently changed on live instead of on test. The password is hardcoded (not my doing) in to their connection string so that would cause the login failure but I'm concerned that the failed login didn't appear in the SQL log. I'm starting to think that it hits windows athentication before it moves to SQL authentication so it never actually gets to try to log in to SQL. Would anyone know if that's the case? I'm trolling the net and I cant find anything on it 🙁