An unhandled exception of type 'System.IO.IOException' occurred in mscorlib.dll

Additional information: The process cannot access the file 'C:\Users\ACER\Desktop\Common-Mistakes-Backup.rtf' because it is being used by another process.

The error appears when I open a file that has been saved or updated, when running the program at the same time. I want users to be able to look at their files whenever they want without the need of closing the program first after it is installed. The problem appear when I try Save or when I try to use Autosave Function that acts as a backup incase of power failure. Here is the code with the problem:

Code:
        ElseIf File.Exists(path) = True Then

            ' Save the contents of the RichTextBox into the file.
            RichTextBox1.SaveFile(path, _
                RichTextBoxStreamType.RichText)

            Timer1.Start()
        End If
Here is the rest of the code:

Code:
    Private Sub SaveRecord()

        'Declare a SaveFileDialog object
        Dim objSaveFileDialog As New SaveFileDialog

        'Set the Save dialog properties
        With objSaveFileDialog
            .DefaultExt = ".rtf"
            .FileName = "Common-Mistakes"
            .Filter = "Word Document (*.rtf)|*.rtf|(*.txt)|*.txt|All files (*.*)|*.*"
            .FilterIndex = 1
            .OverwritePrompt = True
            .Title = "SaveAs File Dialog"
        End With

        Dim path As String = (My.Computer.FileSystem.SpecialDirectories.MyDocuments & "\Common-Mistakes.rtf")

        ' This text is added only once to the file.
        If File.Exists(path) = False Then

            If objSaveFileDialog.ShowDialog = Windows.Forms.DialogResult.OK Then
                Try
                    Dim filePath As String = System.IO.Path.Combine( _
                        My.Computer.FileSystem.SpecialDirectories.MyDocuments, _
                        objSaveFileDialog.FileName)

                    ' Save the contents of the RichTextBox into the file.
                    RichTextBox1.SaveFile(filePath, _
                        RichTextBoxStreamType.RichText)

                Catch fileException As Exception
                    Throw fileException
                End Try
            End If

        ElseIf File.Exists(path) = True Then

            ' Save the contents of the RichTextBox into the file.
            RichTextBox1.SaveFile(path, _
                RichTextBoxStreamType.RichText)
            MessageBox.Show("You have already saved on that location!", "File Already Saved!", MessageBoxButtons.OK)

        End If

        'Clean up
        objSaveFileDialog.Dispose()
        objSaveFileDialog = Nothing
    End Sub
    Private Sub AutosaveFile()

        Dim path As String = (My.Computer.FileSystem.SpecialDirectories.Desktop & "\Common-Mistakes-Backup.rtf")

        ' This text is added only once to the file.
        If File.Exists(path) = False Then

                      ' Save the contents of the RichTextBox into the file.
            RichTextBox1.SaveFile(path, _
                RichTextBoxStreamType.RichText)

        ElseIf File.Exists(path) = True Then

            ' Save the contents of the RichTextBox into the file.
            RichTextBox1.SaveFile(path, _
                RichTextBoxStreamType.RichText)

            Timer1.Start()
        End If
    End Sub
    'End of Save Functions Sections.'