Loading a form from another project as an mdi child

I'm developing a plugin architecture which appears to be working in all respects except when I attempt to load a form parsed into my main project as an mdi child form.

I can load the same form and display it modally but when I attempt to set set its parent property to my mdi parent form, I get the following error...

"Cannot add a top level control to a control".

Any ideas?  See my code below...

This is the code behind the form in my Main application...

<Serializable()> _
Public Class Form1
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents Splitter1 As System.Windows.Forms.Splitter
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Label1 = New System.Windows.Forms.Label
        Me.Splitter1 = New System.Windows.Forms.Splitter
        Me.SuspendLayout()
        '
        'Label1
        '
        Me.Label1.Dock = System.Windows.Forms.DockStyle.Left
        Me.Label1.Location = New System.Drawing.Point(0, 0)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(112, 486)
        Me.Label1.TabIndex = 0
        Me.Label1.Text = "MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM M" & _
        "AIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM M" & _
        "AIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM M" & _
        "AIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM M" & _
        "AIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM M" & _
        "AIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM MAIN FORM M" & _
        "AIN FORM "
        '
        'Splitter1
        '
        Me.Splitter1.Location = New System.Drawing.Point(112, 0)
        Me.Splitter1.Name = "Splitter1"
        Me.Splitter1.Size = New System.Drawing.Size(3, 486)
        Me.Splitter1.TabIndex = 1
        Me.Splitter1.TabStop = False
        '
        'Form1
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(632, 486)
        Me.Controls.Add(Me.Splitter1)
        Me.Controls.Add(Me.Label1)
        Me.IsMdiContainer = True
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private tc As TestInterface.iTestClass
    Private f As Form

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'tc = CreateObject("TestClass")
        'tc = GetObject("C:\Documents and Settings\James\My Documents\Visual Studio Projects\TestSolution\ClassLibrary\bin\ClassLibrary.dll", "TestClass")
        tc = New ClassLibrary.TestClass

        f = New ClassLibrary.TestForm

        f.Parent = Me
        f.Dock = DockStyle.Fill
        f.ShowDialog(Me)
    End Sub
End Class



'THIS IS MY TEST INTERFACE
Public Interface iTestClass
    ReadOnly Property Form()



End Interface





'THIS IS MY TEST PLUGIN

'First the implementation of iTestClass
Public Class TestClass
    Implements TestInterface.iTestClass



    Public ReadOnly Property Form() As Object Implements TestInterface.iTestClass.Form
        Get
            Return New TestForm
        End Get
    End Property
End Class


'Then the form i'm trying to parse into the main application
<Serializable()> _
Public Class TestForm
    Inherits System.Windows.Forms.Form

#Region " Windows Form Designer generated code "

    Public Sub New()
        MyBase.New()

        'This call is required by the Windows Form Designer.
        InitializeComponent()

        'Add any initialization after the InitializeComponent() call

    End Sub

    'Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub

    'Required by the Windows Form Designer
    Private components As System.ComponentModel.IContainer

    'NOTE: The following procedure is required by the Windows Form Designer
    'It can be modified using the Windows Form Designer.  
    'Do not modify it using the code editor.
    Friend WithEvents Label1 As System.Windows.Forms.Label
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Label1 = New System.Windows.Forms.Label
        Me.SuspendLayout()
        '
        'Label1
        '
        Me.Label1.Location = New System.Drawing.Point(0, 24)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(472, 256)
        Me.Label1.TabIndex = 0
        Me.Label1.Text = "THIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR " & _
        "THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FOR" & _
        "M THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST F" & _
        "ORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST " & _
        "FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST" & _
        " FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TE" & _
        "ST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY T" & _
        "EST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY " & _
        "TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS M" & _
        "Y TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS " & _
        "MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS" & _
        " MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS " & _
        "IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS" & _
        " IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THI" & _
        "S IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM T" & _
        "HIS IS MY TEST FORMTHIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORM" & _
        "THIS IS MY TEST FOR THIS IS MY TEST FORM THIS IS MY TEST FORMTHIS IS MY TEST FOR" & _
        " THIS IS MY TEST FORM THIS IS MY TEST FORM THIS IS MY TEST FORM"
        '
        'TestForm
        '
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(480, 318)
        Me.Controls.Add(Me.Label1)
        Me.Name = "TestForm"
        Me.Text = "TestForm"
        Me.ResumeLayout(False)

    End Sub

#End Region

    Private Sub TestForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub
End Class