ActiveX Controls don't display in IE6 XP SP2

I have an intranet app that requires various ActiveX
controls including Microsoft's msxml3.dll and mscomct2.ocx
(calendar control). Both the above controls are already
loaded and registered on the XP SP2 system, so
downloading/installing is not a problem (Tools:Manage Add-
ons shows the controls are loaded and enabled). The
msxml3.dll works fine, but the calendar control does not
display (a red X is displayed instead). Further, when
attempting to script the control (e.g.,
form1.calendar1.year = 2003) an error is generated
indicating form1.calendar1 is undefined, which tells me
the control was not instantiated. I have the ActiveX
security settings as loose as possible (Run ActiveX
controls and Plugins enabled; Initialize and script
ActiveX controls not marked as safe enabled; Active
Scripting enabled; Script ActiveX controls marked as safe
for scripting enabled). I have other non-MS controls that
instantiate and display properly (Crystal Reports
crviewer.dll and FarPoint spreadsheet control). The
calendar control works fine on pre-SP2 XP systems.
Any ideas/clues?