I have a number of desktop applications all built using .net framework 3 which seem to go through phases of intermittently throwing an error when connecting to our database. The error is a simple "login failed for user 'sa'" as if the user name is incorrect but as it works the majority of the time it obviously is not.

I am using the sqlClient.sqlClientConnection with native drivers with all my applications and connecting to a sql2005 database which is mirrored to a backup.

Has anyone heard of or experiencing anything like this before? this is proving a tough one to diagnose!