How to send keystroke to 3rd party desktop application

Question

I am facing problem  to automate a desktop aplication this code  work's only for 2 or 3 days after this send error is access denied but forground windows is focused. and activated ....i run this as admin.and also tried sendkeys.send,sendkey.sendwait.. but problem remains same....

 

namespace WindowsFormsApplication8 

{ public partial class Form1 : Form 

{ public Form1()

 {

 InitializeComponent();

 } 

[DllImport("User32.dll", SetLastError = true)] 

public static extern IntPtr FindWindow(String lpClassName, String lpWindowName);

 private void button1_Click(object sender, EventArgs e)

 {

 try

 { 

Process myproc= Process.GetProcessesByName("name").FirstOrDefault(); 

if (myproc!= null)

 { var ffCondition = new PropertyCondition(AutomationElement.ProcessIdProperty, myproc.Id); 

var ffWindows = AutomationElement.RootElement.FindAll(TreeScope.Children, ffCondition);

 var soWindow = ffWindows.Cast<AutomationElement>().FirstOrDefault(w => w.Current.Name.Contains("title of window ")); 

if (soWindow != null) 

{

 var soWindowPattern = soWindow.GetCurrentPattern(WindowPattern.Pattern) as WindowPattern;

 if (soWindowPattern != null) 

{

 // Restore window (activating it). 

    soWindowPattern.SetWindowVisualState(WindowVisualState.Normal);

 Thread.Sleep(100);

 // Close window. //soWindowPattern.Close(); 

SendKeys.Send("{f1}");

 //System.Windows.Forms.SendKeys.SendWait("{f1}");

 //string send = System.Windows.Input.Key.F1.ToString();

 //SendKeys.SendWait(send);

 var soWindow1 = ffWindows.Cast<AutomationElement>().FirstOrDefault(w => w.Current.Name.Contains("another child window ")); 

}

 }

 }

 }

 catch (Exception ex)

 {

 MessageBox.Show(ex.ToString());

 }

 }

 }

 }