************** Testo dell'eccezione **************

System.UnauthorizedAccessException: Accesso al percorso 'D:\****\a.txt' negato.

   in System.IO.__Error.WinIOError(Int32 errorCode, String maybeFullPath)

   in System.IO.FileStream.Init(String path, FileMode mode, FileAccess access, Int32 rights, Boolean useRights, FileShare share, Int32 bufferSize, FileOptions options, SECURITY_ATTRIBUTES secAttrs, String msgPath, Boolean bFromProxy)

   in System.IO.FileStream..ctor(String path, FileMode mode, FileAccess access, FileShare share, Int32 bufferSize, FileOptions options)

   in System.IO.StreamWriter.CreateFile(String path, Boolean append)

   in System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding, Int32 bufferSize)

   in System.IO.StreamWriter..ctor(String path, Boolean append, Encoding encoding)

   in Microsoft.VisualBasic.FileIO.FileSystem.WriteAllText(String file, String text, Boolean append, Encoding encoding)

   in Microsoft.VisualBasic.MyServices.FileSystemProxy.WriteAllText(String file, String text, Boolean append)

   in Folder_Customizer__01_.Form1.Button3_Click(Object sender, EventArgs e)

   in System.Windows.Forms.Control.OnClick(EventArgs e)

   in System.Windows.Forms.Button.OnClick(EventArgs e)

   in System.Windows.Forms.Button.WndProc(Message& m)

   in System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)

   in System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)

   in System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

 

...qui va il tuo codice che hai riportato

 

catch exc as exception

 

end try