Login failed when connecting to SQL database

When trying to connect BillQuick to a SQL Server database, user gets this error - 

"Login failed for user 'username'. The user is not associated with a trusted SQL Server connection."

This problem is typically due to the fact that your SQL Server has been configured to operate in "Windows Authentication" mode and doesn't allow the use of SQL accounts. 

Follow these steps to resolve the problem:

1. Log in as Local Administrator to your machine (SQL Server instance machine) and log in to SQL Server instance using Windows Authentication.
2. Change the Authentication Mode of the SQL Server from "Windows Authentication Mode (Windows Authentication)" to "Mixed Mode (Windows Authentication and SQL Server Authentication).
3. Enable 'sa' login.
4. Restart the service.