One of the problem I recently ran into was that my project had refactored the business logic and the dataaccess out into a seperate assembly. The problem i ran into was that i kept getting connected to the old database i used before and not the new one i installed on lmy local machine. I stumbled across this blog entry explaining that my connectionstring was being saved several place. I followed this simple receipe and voila, it works.

http://goneale.com/2009/03/26/untie-linq-to-sql-connection-string-from-application-settings/