[O] Sort error [9.0.9 (9.0.9-88-g251f88-elpa @ /home/someone/.emacs.d/elpa/org-20170821/)]

[Allen Choong]

Expect to sort the items according to "todo order" which has no issue previously. But now it fails. Not only "todo order" but also "alpha", "numeric", and so on, except "clocking".

With a file contains this,

==============

* test

** TODO test2

** DONE test3

   CLOSED: [2017-08-28 Mon 15:51]

** test4

==============

I put my cursor at "*test", and do a "C-c ^" (org-sort), then type "o" (todo(o)rder), but is shows 

```

org-sort-entries: Symbol’s function definition is void: org-clocking-buffer

```

However, if I do the sorting with "clocking" first, then all the other sort will work fine, until I restart the emacs.

Regards,
Allen