Why didn´t work my OpenFileDialog : I try to open a textdocument and than i get the message: invalid file format from the try-catch. I use Visual Studio 2015 with Visual C# and Windows Forms Application.

Here my code for the open function:

    private void openToolStripMenuItem_Click(object sender, EventArgs e)
    {
        try { 
        // Create an OpenFileDialog to request a file to open.
        OpenFileDialog openFile1 = new OpenFileDialog();

        // Initialize the OpenFileDialog to look for RTF files.

        openFile1.Filter = "Text Files (*.txt)|*.txt| RTF Files (*.rtf)|*.rtf| All (*.*)|*.*";

        // Determine whether the user selected a file from the OpenFileDialog.
        if (openFile1.ShowDialog() == System.Windows.Forms.DialogResult.OK &&
           openFile1.FileName.Length > 0)
        {
            // Load the contents of the file into the RichTextBox.
            TextBox.LoadFile(openFile1.FileName);
        }
        }
        catch (Exception a)
        {
            MessageBox.Show(a.Message);
        }
    }//end open

I hope you can help me with friendly wishes sniffi.