Thank you for the quick response.
However, I had gone there prior to posting the question. What I am seeing
are the default calendars and a calendar I added. However, there are other
calendars that were added by a client who gave me this schedule. There are
about 4 or 5 of these added calendars. None of these calendars are showing up
in the tools/organize/calendar tab. And, none of these have been assigned to
an activity (with the exception of the one I added). Why aren't these other
calendars showing up in the above add/remove tab?