Looking online there are a number of conflicting suggestions, so your mileage may vary with the following suggestions:
- Check the user and the Database are on the same domain
- When entering the username do not include the domain/ element, just use the actual user name
- Get your DBA to check the SQL Server logs for login failure information; the error state may provide detail on the actual reason for the failure. Also confirm that the Database is configured to accept connections from that domain
- Try setting the domain to be corp.global.level3.com