I am sorry to hear that you have problems with running our examples. The things that come to my mind are:
1. Try to install the latest version of the Silverlight tools from here http://www.microsoft.com/downloads/details.aspx?FamilyId=c22d6a7b-546f-4407-8ef6-d60c8ee221ed&displaylang=en
if you don't have it or it is not the latest version.
2. Check if you have .NET Framework 3.5 installed.
3. If nothing helps, you can try to reinstall the Visual Studio, maybe the problem is with some kind of add- on.
About the second question - the control is RadTreeView.
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