Namespace error in wpf

No, thank you. Please solve it by yourself. Element is your type, so make sure you name it properly and reference the assembly where it is defined. You did not give us any information on it. (And don't bother to do so, better learn some programming basics first, in particular, namespaces, assemblies and references; right now, you don't have a clue, so better don't jump into programming if you did not bother to learn the basics.)
—SA