I have encountered same problem reported by Rachel (and others). While I have
not tried the solutions offered in this thread, I did discover the trigger
event that caused the flyout menus to disappear.
In my case, if I opened an email which caused the 'Word will open as your
email editor' dialog (can't quite remember the exact wording) to pop up, then
the flyout menus would disappear until I closed Word and Outlook. This was a
repeatable sequence not related to any particular document (even happened
with a blank new document). Would happen if Word was already open with Table
menu flyouts visible/functioning correctly, but as soon as Outlook did its
thing, then good-bye flyouts.
I have Acrobat Pro 6, so will try fix below. However, for whatever reason, I
think the Outlook connection is the more likely culprit.
Cheers
Rex