Talvez, puedas mejorar un poco la forma de recorre los textbox, por ejemplo
Código ASP:
Ver originalPrivate Sub ChangeBtn_Click(ByVal sender As Object, ByVal e As EventArgs)
Dim c As Control
Dim c2 As Control
For Each c In Page.Controls
If c.Controls.Count > 0 Then
For Each c2 In c.Controls
If c2.GetType.ToString = "System.Web.UI.WebControls.TextBox" Then
MySpan.InnerHtml = CType(c2, TextBox).Text
CType(c2, TextBox).Text = ""
End If
Next
End If
Next
End Sub