Is it just me? or am I doing something wrong?

c_wbFavouriteA is a WebBrowser control

if in my code I do this at some stage.....

Code:
System.Uri siteUri = new System.Uri("http://www.yahoo.com");
c_wbFavouriteA.Stop();
c_wbFavouriteA.Navigate(siteUri);
and later do this....

Code:
System.Uri siteUri = new System.Uri("http://www.google.com");
c_wbFavouriteA.Stop();
c_wbFavouriteA.Navigate(siteUri);
Google doesn't load into the control.

Am I doing something wrong? or might there be something wrong with my .NET installation?