Are you using SQL Server or Windows authentication in your application?

>We have been having this problem the last few days where every so often when we run our app
>or even try to connection we get:
>
>

>Login failed for user ''. The user is not associated with a trusted SQL Server connection.
> (Microsoft SQL Server, Error: 18452)
>

>
>No changes have been made and the server machine is running normally.
>
>Anyone?