stockpicker not able to be added

I am watching the first video, and when I tried to add "security picker" from toolbox,

I just only see following error message and cannot add it.

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"The following reference has been added to the project:
"StockSharp.Xaml, Version=4.4.14.0, Culture=neutral, PublickKeyToken=null"

In order to user types from the new reference, press OK to restart the XAML Designer. After the XAML Designer restarts, re-create the control on the artboard.
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I have close the MainWindow.xaml and reopened, but not successful.