Visual Basic.NET - BC 30002 No esta definido el tipo 'Form2'.

Imports System.Runtime.InteropServices

Public Class FormPrincipal

#Region "FUNCIONALIDADES DEL FORMULARIO"

    'RESIZE DEL FORMULARIO- CAMBIAR TAMAÑO

    Dim cGrip As Integer = 10

    Protected Overrides Sub WndProc(ByRef m As Message)

        If (m.Msg = 132) Then

            Dim pos As Point = New Point((m.LParam.ToInt32 And 65535), (m.LParam.ToInt32 + 16))

            pos = Me.PointToClient(pos)

            If ((pos.X _

                        >= (Me.ClientSize.Width - cGrip)) _

                        AndAlso (pos.Y _

                        >= (Me.ClientSize.Height - cGrip))) Then

                m.Result = CType(17, IntPtr)

                Return

            End If

        End If

        MyBase.WndProc(m)

    End Sub

    '----------------DIBUJAR RECTANGULO / EXCLUIR ESQUINA PANEL

    Dim sizeGripRectangle As Rectangle

    Dim tolerance As Integer = 15

    Protected Overrides Sub OnSizeChanged(ByVal e As EventArgs)

        MyBase.OnSizeChanged(e)

        Dim region = New Region(New Rectangle(0, 0, Me.ClientRectangle.Width, Me.ClientRectangle.Height))

        sizeGripRectangle = New Rectangle((Me.ClientRectangle.Width - tolerance), (Me.ClientRectangle.Height - tolerance), tolerance, tolerance)

        region.Exclude(sizeGripRectangle)

        Me.PanelContenedor.Region = region

        Me.Invalidate()

    End Sub

    '----------------COLOR Y GRIP DE RECTANGULO INFERIOR

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)

        Dim blueBrush As SolidBrush = New SolidBrush(Color.FromArgb(244, 244, 244))

        e.Graphics.FillRectangle(blueBrush, sizeGripRectangle)

        MyBase.OnPaint(e)

        ControlPaint.DrawSizeGrip(e.Graphics, Color.Transparent, sizeGripRectangle)

    End Sub

#End Region

#Region "Arrastrar Formulario"

    <DllImport("user32.DLL", EntryPoint:="ReleaseCapture")>

    Private Shared Sub ReleaseCapture()

    End Sub

    <DllImport("user32.DLL", EntryPoint:="SendMessage")>

    Private Shared Sub SendMessage(ByVal hWnd As System.IntPtr, ByVal wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Integer)

    End Sub

    Private Sub PanelBarraTitulo_MouseMove(sender As Object, e As MouseEventArgs) Handles PanelBarraTitulo.MouseMove

        ReleaseCapture()

        SendMessage(Me.Handle, &H112&, &HF012&, 0)

    End Sub

#End Region

#Region "Comportamiento del Formulario"

    Private Sub BtnCerrar_Click(sender As Object, e As EventArgs) Handles BtnCerrar.Click

        Application.Exit()

    End Sub

    Dim lx, ly As Integer

    Dim sw, sh As Integer

    Private Sub BtnMinimizar_Click(sender As Object, e As EventArgs) Handles BtnMinimizar.Click

        Me.WindowState = FormWindowState.Minimized

    End Sub

    Private Sub BtnMaximizar_Click(sender As Object, e As EventArgs) Handles BtnMaximizar.Click

        lx = Me.Location.X

        ly = Me.Location.Y

        sw = Me.Size.Width

        sh = Me.Size.Height

        BtnMaximizar.Visible = False

        BtnRestaurar.Visible = True

        Me.Size = Screen.PrimaryScreen.WorkingArea.Size

        Me.Location = Screen.PrimaryScreen.WorkingArea.Location

    End Sub

    Private Sub BtnRestaurar_Click(sender As Object, e As EventArgs) Handles BtnRestaurar.Click

        Me.Size = New Size(sw, sh)

        Me.Location = New Point(lx, ly)

        BtnMaximizar.Visible = True

        BtnRestaurar.Visible = False

    End Sub

#End Region

    'METODO DE ABRIR FORMULARIO

    Private Sub AbrirFormEnPanel(Of Miform As {Form, New})()

        Dim Formulario As Form

        Formulario = PanelFormularios.Controls.OfType(Of Miform)().FirstOrDefault() 'Busca el formulario en la coleccion

        'Si form no fue econtrado/ no existe

        If Formulario Is Nothing Then

            Formulario = New Miform()

            Formulario.TopLevel = False

            Formulario.FormBorderStyle = FormBorderStyle.None

            Formulario.Dock = DockStyle.Fill

            PanelFormularios.Controls.Add(Formulario)

            PanelFormularios.Tag = Formulario

            AddHandler Formulario.FormClosed, AddressOf Me.CerrarFormulario

            Formulario.Show()

            Formulario.BringToFront()

        Else

            Formulario.BringToFront()

        End If

    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click

        AbrirFormEnPanel(Of Form1)()

        Button1.BackColor = Color.FromArgb(12, 61, 92)

    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click

        AbrirFormEnPanel(Of Form2)()

        Button2.BackColor = Color.FromArgb(12, 61, 92)

    End Sub

    Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click

        AbrirFormEnPanel(Of Form3)()

        Button3.BackColor = Color.FromArgb(12, 61, 92)

    End Sub

#Region "METODO/EVENTO AL CERRAR FORMS"

    Private Sub CerrarFormulario(ByVal sender As Object, ByVal e As FormClosedEventArgs)

        'CONDICION SI FORMS ESTA ABIERTO

        If (Application.OpenForms("Form1") Is Nothing) Then

            Button1.BackColor = Color.FromArgb(4, 41, 68)

        End If

        If (Application.OpenForms("Form2") Is Nothing) Then

            Button2.BackColor = Color.FromArgb(4, 41, 68)

        End If

        If (Application.OpenForms("Form3") Is Nothing) Then

            Button3.BackColor = Color.FromArgb(4, 41, 68)

        End If

    End Sub

#End Region

End Class