The 'clr-namespace' URI refers to a namespace that is not included in the assembly

Question

I\'m trying to include in my XAML some classes which convert values. However, I\'m getting the following error when I compile:

Undefined CLR namespac

Answer 1

I just solved this by changing the target from x64 to x86. Apparently Visual Studio is 32bit process and it's unable to load 64bit assemblies, and if your assembly is targeting x64 platform and you adding some custom control visual studio is unable to load it and throws this message.