Как очистить весь вменяемый текст на странице

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Мой код не распознает текстовые поля Gettype

Что я уже пробовал:

Dim ctrl As Control
For Each ctrl In Me.Controls
    If (ctrl.GetType() Is GetType(TextBox)) Then
        Dim txt As TextBox = CType(ctrl, TextBox)
        txt.Controls.Clear()
    End If
Next

Мой html-код...

<div>
          Doctor :<input type="text" runat="server" name="DoctorName" size="20" class="TxtBox" id="txtDoctorName" tabindex="3" />
          <input type="text" runat="server" name="DoctorAddress" size="20" id="txtDoctorAddress" class="TxtBox" tabindex="4" />
          <input type="text" runat="server" name="SuiteAddress" size="20" id="txtSuiteAddress" class="TxtBox" tabindex="5" />
          <input type="text" runat="server" name="City" size="20" id="txtCity" class="TxtBox" tabindex="6" />
          <input type="text" runat="server" name="State" size="5" id="txtState" class="TxtBox" tabindex="7" />
          <input type="text" runat="server" name="Zip" size="10" id="txtZipCode" class="TxtBox" tabindex="8" />
          <br />

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