The solution:

xmlns:df="clr-namespace:System.Windows.Controls; assembly=System.Windows.Controls.Data.DataForm.Toolkit"

should have been like this:

xmlns:df="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Data.DataForm.Toolkit"

Yeah, right.

For an explanation, see my next message.



>Although I would have much rather been at the beachfront bonfire party with my peeps, I had to get a relatively simple Silverlight 4.0 LOB project done. So I stayed home, unhappily typing XAML like this:
>
>xmlns:df="clr-namespace:System.Windows.Controls; assembly=System.Windows.Controls.Data.DataForm.Toolkit"
>
>I build the project. No errors! Great!
>
>And then I run it. Winding...winding...winding... Ahh!!! Now what? I get a XamlParseException:
>
>The type 'DataForm' was not found because 'clr-namespace:System.Windows.Controls; assembly=System.Windows.Controls.Data.DataForm.Toolkit' is an unknown namespace. [Line: 15 Position: 34]
>
>Since my VS help doesn't work, like, AT ALL, I go to Google (which I would probably do anyway, given the relatively unhelpful ways of Microsoft Help.) However, after 10 minutes of googling I still don't find any good answers to this particular problem.
>
>But the error is clearly in that line. Postion 34 starts with "ols:"
>
>What's wrong with "ols"? What's wrong with me? What's wrong with Microsoft? What's WRONG with this line:
>
>xmlns:df="clr-namespace:System.Windows.Controls; assembly=System.Windows.Controls.Data.DataForm.Toolkit"
>
>For an answer, see my next message.