tao_ifr seems to fail to load some IDLs which conatain nested 
structures and unions definitions. Strangely it processes without error
declaration like this:

...
struct event4d {
  double            t;
  point3d           p;
  sequence<event4d> events;

  union EventValues switch(long)
  {
    case 0:
      long              longValue;
    case 1:
      sequence<event4d>	eventValue;
  } value;
};
...

but fails on bigger IDL files which have more structures and unions.
IDL files I have are too big to be inserted in here, I will send them 
via email upon your request. 

tao_ifr gives following messages:

d:\bbms\idlchk>tao_ifr -ORBInitRef 
InterfaceRepository=corbaloc::FILV3446:2298/InterfaceRepository mgrpfemsmomd.idl
idli_a02900.cc
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor.cpp:1562) 
ifr_adding_visitor::element_type - lookup_id failed
(2012|2900) EXCEPTION, visit_sequence
system exception, ID 'IDL:omg.org/CORBA/BAD_PARAM:1.0'
TAO exception, minor code = 0 (unknown location; unspecified errno), completed 
= NO

(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor_structure.cpp:113) 
ifr_adding_visitor_structure::visit_scope - failed to accept visitor
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor_structure.cpp:173) 
ifr_adding_visitor_structure::visit_structure - visit_scope failed
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor.cpp:90) 
ifr_adding_visitor::visit_scope - failed to accept visitor
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor.cpp:223) 
ifr_adding_visitor::visit_module - visit_scope failed
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor.cpp:90) 
ifr_adding_visitor::visit_scope - failed to accept visitor
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\ifr_adding_visitor.cpp:1249) 
ifr_adding_visitor::visit_root - visit_scope failed
(C:\ACE_wrappers\TAO\orbsvcs\IFR_Service\be_produce.cpp:278) BE_produce - 
failed to accept visitor
Fatal Error - Aborting