System.Windows.Forms.SendKeys

hi,
   Iam having a small problem in using the System.Windows.Forms.SendKeys API to send input to an active appication. I have an exe file for adding two numbers. I have to give input to that and get the result. My code ( which i have given below) works sometime and does not work someother time. It gives and unhandled exception error. can anyone tell me why?
 
   Dim myProcess As Process = New Process()
   myProcess.StartInfo.FileName = "Addition.exe"
   myProcess.StartInfo.WindowStyle = ProcessWindowStyle.Normal
   myProcess.EnableRaisingEvents = True
   myProcess.Start()
    Try
         If myProcess.Responding Then
           System.Windows.Forms.SendKeys.SendWait("2")
           System.Windows.Forms.SendKeys.SendWait("{ENTER}")
           System.Windows.Forms.SendKeys.SendWait("3")
           System.Windows.Forms.SendKeys.SendWait("{ENTER}")
           System.Windows.Forms.SendKeys.Send("{ENTER}")
           System.Windows.Forms.SendKeys.Flush()
         Else
            myProcess.Kill()
        End If

-sendhil