Detect a process exit in 64bit OS

My Unity game wants to start a separate program in Windows and should restore it self when that program has finished running.

Here's my code:

            ----Inside GUI Button----
             try
             {
                 ProcessStartInfo startInfo = new ProcessStartInfo ();
                 startInfo.FileName = "notepad.exe";
                 
                 Process p = new Process ();
                 p.StartInfo = startInfo;
                 p.EnableRaisingEvents = true;
                 p.Exited += HandlePExited;
                 p.Start ();
             }
             catch (System.Exception e)
             {
                 UnityEngine.Debug.Log ("Exception :: "+e.Message.ToString ());
             }
             ------------------------

             void HandlePExited (object sender, EventArgs e)
             {
                 UnityEngine.Debug.Log ("exited!");
             }

t$$anonymous$$s method works only when i'm running the application on a 32bit mac$$anonymous$$ne. It simply doesn't trigger "HandlePExited" event in 64bit.

I've also tried using System.Diagnostics.Processes.GetProcesses() to find the process by name and that method also works for 32bit only. In 64bit mode it always says

 InvalidOperationException: Process has exited, so the requested information is not available.
 System.Diagnostics.Process.get_ProcessName ()

Running: Unity 4.1.5f1, Windows 7, 32bit final build

any help would be great. Thanks