Following up on a note about Visual Studio 2010 crashing at my previous post, this is the XAML that crashes VS2010 when opened up in a Silverlight project: <UserControl x:Class="SilverlightApplication1.MainPage"   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"   ...

I just had some big trouble troubleshooting the Visual Studio / XAML compiler error message: The tag XXX does not exist in XML namespace ‘clr-namespace:YYY’ It turned out this occurred because I had a Silverlight library with Assembly name X and default namespace X (at properties pane), but was using it from a demo project [...]