error message "Login failed for user DOMAIN\USERNAME"?

You'll have to create an account in SQL Server for the aspnet user.

1. Start enterprise manager-> expand the server-> select security->Right-click in the right view and select new login.
2. enter the DOMAIN\USERNAME and select your database as the default database of the user at the bottom of the page.
3. Select last tab Database Access -> select your database, and add the db_datareader and db_datawriter policies to your user.