Disabling Outlook's context menu item

[Vladimir Chtchetkine]

How can I do this? I "event" commandbars's "update",
find "Context Menu" command bar, loop through its items
and disable those that I need to disable : Enabled
(false). I verify that Enable call succeeds but items are
appeared as enabled. Same technic works fine for toolbar
buttons and main menu items. That's context menu that
gives me headaches.
Second (kind of related) question is on Actions. I was
trying to simply delete some Action items from the
_MailItem instance but Delete() fails. Again, what's the
trick here? I would appreciate any feedback.

TIA,

Vladimir