Error: 'Cannot create unknown type '{clr-namespace:NameSpace.Properties}Settings'.'

I had set the file's "Build Action" property to "Resource". When I changed it to "Page" the problem was resolved.

Keep your "Build Action" property to "Resource" and just change this row:

xmlns:properties="clr-namespace:Kavand.UI.Properties"

with this:

xmlns:properties="clr-namespace:Kavand.UI.Properties;assembly=Kavand.UI"

Just posting another potential solution, because i just recently stumbled over this exception.

It could be that your referenced class-cefinition (in your case Kavand.UI.Properties.Settings) does not use public-access-modifier.

So in my case i could solve this problem by writing public before the class definition.