I have a central connect.ini file that's used here which has TrustedAuto specified so that login is seemless. Although not the most secure, I required one computer to prompt for credentials. I've tried modifying the local connect.ini file to show the ServerName and DatabaseName lines with relevant values and this does prompt but the correct username and password combination simply results in an "Invalid user name/password" message.

Can you not have a mix of trusted and non-trusted connections?