if (LogonUser(UserLogon, Domain, UserPassword, LOGON32_LOGON_INTERACTIVE, LOGON32_PROVIDER_DEFAULT, ref ptrToken) != 0)  
   {  
[.........CODICE PER LA COPIA..........]
 if (DuplicateToken(ptrToken, 2, ref ptrTokenDuplicate) != 0)  
      {  
         WindowsIdentity UserIdentity = new WindowsIdentity(ptrTokenDuplicate);  
         _CtxImpersonation = UserIdentity.Impersonate();  
         if (null != UserIdentity) return true;  
      }  
   }