Error upon running.

[floccipier]

Hi I get this eorry upon running.. any idea how to fix?

System.ArgumentException
HResult=0x80070057
Message=Assembly 'C:\Users\SAM\Documents\GitHub\Autodesk-Inventor-WPF-Dockable-Window\WPFDockableWindow\obj\Debug\WPFDockableWindow.dll' doesn't contain any UserControl types.
Source=UserControlTestContainer
StackTrace:
at Microsoft.VisualStudio.Tools.UserControlTestContainer.UserControlTestContainer_Load(Object sender, EventArgs e)
at System.Windows.Forms.Form.OnLoad(EventArgs e)
at System.Windows.Forms.Form.OnCreateControl()
at System.Windows.Forms.Control.CreateControl(Boolean fIgnoreVisible)
at System.Windows.Forms.Control.CreateControl()
at System.Windows.Forms.Control.WmShowWindow(Message& m)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.Form.WmShowWindow(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)