tbgg, you are a genious!  Just as you suggested I went through the
appoinments between the dates that the error message appeared and sure enough
when I clicked on the one that was causing the problem, I got the error
message.  In case anyone has the same problem here are the exact steps to
follow:

1. Bring up your Calendar.
2. Click on "View" at the top of the window.
3. Click on "Arrange By".
4. Click on "Current View".
5. Click on "By Category".
6. Click on all the reminders within the dates that you started having the
problem.  When you get the one that brings up the Error Message, delete it  
(you might want to write it down if you want to re-enter the reminder).  You
might have more than one message causing the problem so I would continue
checking the reminders just in case.
7. When you are done, to bring the view back to normal (normal for me) click
on "View".
8. Click on "Arrange By".
9. Click on "Current View" at the bottom of the menu.
10. Click on "Day/Week/Month" and you should be back to the Default setting.

I hope this helps!  I had this happen twice now and I am surprised that
Microsoft does not have more help on this since it seems to be such an easy
fix when you know how to do it.  Thanks again tbgg! :)