Make sure your database connection info is correct in your user.config file. It should look something like this:
<add key="MSSQLConnectionString" value="server=yourservername;UID=yourdatabaseusername;PWD=yourdatabaseuserpassword;database=yourdatabasename" />
You must open your web.config, add a space to the bottom and then save it again to get your application pool to reset so the user.config will be read again. You must do this each time you change your user.config to apply the changes immediately.