title: Silverlight 3: No change but now I am getting "Page Not Found"
body: <p>Had a page that was working fine. Only change I made was to add a datagrid to the page (which also added the xmlns) and all of the sudden I'm getting Page Not Found. Checked the UriMappings. Tried the default nav link. No joy.</p>
  
  <p>Ideas?</p>
  
  <p>UPDATE: The answer was that I had a mock class that was not initializing a collection. See Byrant's answer for a way to save yourself some time.</p>