Errors with WeifenLuo DockManager

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C#

C#4.0

Hello as you can read on my title I have an error on my project and I do not know why I get it, and I have asked on the topic where I got the resource from. Which is: http://www.codeproject.com/KB/cs/SharpFormEditorDemo.aspx?msg=3586200#History12

And my errors are:

//-------------------------------------------------------
private DesignFrame FindDesignerFrame(string text)
{
    Content[] documents = dockManager.Documents;

    foreach (Content C in documents)
    {
        DesignFrame frm = C as DesignFrame; // ERROR HERE
        if (frm != null)
        {
            if (frm.FileName == text)
            {
                return frm;
            }
        }
    }
    return null;
}

//-------------------------------------------------------
private void dockManager_ActiveDocumentChanged(object sender, EventArgs e)
{
    DesignFrame df = dockManager.ActiveDocument as DesignFrame; // ERROR HERE
    if (df != null && m_PropertyWindow != null)
    {
        df.UpdatePropertyWindow();
    }
}

//-------------------------------------------------------
private Content GetContentFromPersistString(string persistString)
{
    if (persistString == typeof(PropertyWindow).ToString())
        return m_PropertyWindow; // ERROR HERE
    else if (persistString == typeof(Toolbox).ToString())
        return m_toolbox;
    else
        return null;
}

and the errors descriptions are:

Cannot convert type 'WeifenLuo.WinFormsUI.Content' to 'SharpDesignerTest.Forms.DesignFrame' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion<br />
<br />
<br />
Cannot convert type 'WeifenLuo.WinFormsUI.Content' to 'SharpDesignerTest.Forms.DesignFrame' via a reference conversion, boxing conversion, unboxing conversion, wrapping conversion, or null type conversion<br />
<br />
Cannot implicitly convert type 'VBDevelop.NET.Forms.PropertyWindow' to 'WeifenLuo.WinFormsUI.Content'	

All help is appreciated thanks! :thumbsup: :D