I remember seeing an emacs 23 git branch at some point, but I looked around
and cannot locate it anymore.  At any rate, this may be a dup, but in emacs
23 inserting diary entries in the agenda does not work.  Here's the patch to
fix it:

diff --git a/lisp/org-agenda.el b/lisp/org-agenda.el
index 23cda50..56c7d62 100644
--- a/lisp/org-agenda.el
+++ b/lisp/org-agenda.el
@@ -5120,7 +5120,7 @@ All the standard commands work: block, weekly etc."
       (unwind-protect
          (progn
            (fset 'calendar-cursor-to-date
-                 (lambda (&optional error)
+                 (lambda (&optional error dummy)
                    (calendar-gregorian-from-absolute
                     (get-text-property point 'day))))
              (call-interactively cmd))
@@ -5307,5 +5307,3 @@ belonging to the \"Work\" category."
 ;; arch-tag: 77f7565d-7c4b-44af-a2df-9f6f7070cff1

 ;;; org-agenda.el ends here
-
-