What doe "Error 5: Missing key value on 'StaticResourceHolder' object." error mean?

I defined a class with a property of Dictionary type, and add items to this property in XAML.
Class definition:

<ContentProperty("TemplateList")>
Public Class ItemTemplateCreator
Inherits DataTemplateSelector

    Public Property TemplateList As New ItemTemplateDictionary()

    ' Some more stuff
End Class
Public Class ItemTemplateDictionary
Inherits Dictionary(Of String, DataTemplate)
End Class

If I do it this way, it works:

<ctr:ItemTemplateCreator x:Key="ItemTemplateCreator"><ctr:ItemTemplateDictionary><DataTemplate x:Key="Name" DataType="ctr:SampleItem1"><TextBlock Text="{Binding Name}" VerticalAlignment="Center"/></DataTemplate></ctr:ItemTemplateDictionary></ctr:ItemTemplateCreator>

But in this way, it does not:

<DataTemplate x:Key="NameTemplate" DataType="ctr:SampleItem1"><TextBlock Text="{Binding Name}" VerticalAlignment="Center"/></DataTemplate><ctr:ItemTemplateCreator x:Key="ItemTemplateCreator"><ctr:ItemTemplateDictionary><StaticResourceExtension x:Key="Name" ResourceKey="NameTemplate"/></ctr:ItemTemplateDictionary></ctr:ItemTemplateCreator>

Actually, it shows the right data in both Cider and Expression Blend, but when running, throws an exception:

'Missing key value on 'StaticResourceHolder' object.' Line number '15' and line position '5'.

Where line 15 is where <ctr:ItemTemplateDictionary> tag is opened.

There is no stack trace, only RewrapException.

What do I do wrong?

Mikhail