I get this error: "file format is not valid"

can this be fixed? if so, could someone point me the way or give me some more code?





Code:
 Dim OpenFile1 As New OpenFileDialog

       


            OpenFile1.Filter = "txt Files (Text Files)|*.txt"


            OpenFile1.Title = "Open a Document."


            If (OpenFile1.ShowDialog = System.Windows.Forms.DialogResult.OK) Then




                RichTextBox1.LoadFile(OpenFile1.FileName)


            End If