impersonateValidUser works well when using administrator account but,for non administrator account ,saying "Access to the path 'xxx' is denied."

hi.

    i am using impersonateValidUser(i will paste my code in the following) to access a folder.i've FINISHED DEVELOPMENT OF PROGRAM and i've DEPLOY and INSTALL on some people's PC.

   for some "good" PC it works well,but for some "bad" PC,only if i login with administrator's account it works well,otherwise  "Access to the path 'xxx' is denied." is told.but for impersonateValidUser part it works works well. for these "bad" PC,if i dont use impersonateValidUser it works,it can access the folder.

   i would like to ask ur help how could i fix the problem.thank u very much for u r kindness help in advance.

my code is:       
        public const int LOGON32_LOGON_INTERACTIVE = 2;
        public const int LOGON32_PROVIDER_DEFAULT = 0;
        WindowsImpersonationContext impersonationContext;
        [DllImport("advapi32.dll")]
        public static extern int LogonUserA(String lpszUserName,
            String lpszDomain,
            String lpszPassword,
            int dwLogonType,
            int dwLogonProvider,
            ref IntPtr phToken);
        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern int DuplicateToken(IntPtr hToken,
            int impersonationLevel,
            ref IntPtr hNewToken);
        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]
        public static extern bool RevertToSelf();
        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        public static extern bool CloseHandle(IntPtr handle); 
        private void undoImpersonation()
        {
            impersonationContext.Undo();
        }
        private bool impersonateValidUser(String userName, String domain, String password)
        {      
            WindowsIdentity tempWindowsIdentity;
            IntPtr token = IntPtr.Zero;
            IntPtr tokenDuplicate = IntPtr.Zero;         
                if (RevertToSelf())
                {
                    if (LogonUserA(userName, domain, password, LOGON32_LOGON_INTERACTIVE,
                        LOGON32_PROVIDER_DEFAULT, ref token) != 0)
                    {
                        if (DuplicateToken(token, 2, ref tokenDuplicate) != 0)
                        {
                            tempWindowsIdentity = new WindowsIdentity(tokenDuplicate);
                            impersonationContext = tempWindowsIdentity.Impersonate();
                            if (impersonationContext != null)
                            {
                                CloseHandle(token);
                                CloseHandle(tokenDuplicate);
                                MessageBox.Show("return true");
                                return true;
                            }
                        }
                    }
                }
                if (token != IntPtr.Zero)
                    CloseHandle(token);
                if (tokenDuplicate != IntPtr.Zero)
                    CloseHandle(tokenDuplicate);   
            return false; 
        }

        private void button1_Click(object sender, EventArgs e)
        {            
            if (impersonateValidUser("username", "domain", "psw"))
            {               
                if (!Directory.Exists(rootComplete))
                {               
                        Directory.CreateDirectory(rootComplete);                   
               
                }     
                File.Copy(filePath, doc, true);              
                undoImpersonation();
            }
            else
            {
                MessageBox.Show("impersonateValidUser,fail login.");               
            }
        }