[DotNetDevelopment] The system cannot find the file specified

[P Square]

I'm trying to run defrag.exe inside a vb.net console app and it's
giving me an error "The system cannot find the file specified" it used
to work so i don't get the problem. Here's my code

Dim oApp As New ProcessStartInfo

oApp.FileName = "c:\windows\system32\defrag.exe"
oApp.Arguments = "/C"
oApp.CreateNoWindow = True

Dim oProcess As Process = Process.Start(oApp)

I even tried using shell command and no luck but if I enter defrag in
command prompt it works? It looks like the console app doesn't see c:
\windows\system32\defrag.exe

Please Help !!!