Ensure you are running in mixed authentication mode. The 'sa' account is used on the eiserver to access the DB.
Check your settings as follows.
1. Right Click on your Server in SQL Enterprise Manager (the server could be named (local) (Windows NT)) where local could also be your computer's name , e.g. (webserver) (Windows NT)
2. Select Properties from the Dialog Box that is displayed
3.SQL Server Properties will appear, select the Security Tab from the list of tabs.
4. In the Security Tab, the Authentication can be SQL Server and Windows or Windows only , select SQL Server and Windows . Then Click the 'OK' button to apply the changes made, if you made any changes.
hope this helps.