FWIW I do not see this issue on the latest version of org on the master
(dev) branch.

Based on the backtrace, it looks like for some reason comment-start-skip is
nil in your emacs session.

Here's the definition of org-agenda-skip:

(defun org-agenda-skip ()
  "Throw to `:skip' in places that should be skipped.
Also moves point to the end of the skipped region, so that search can
continue from there."
  (let ((p (point-at-bol)) to)
    (when (or
  (save-excursion (goto-char p) (looking-at comment-start-skip))
  (and org-agenda-skip-archived-trees (not org-agenda-archives-mode)
(get-text-property p :org-archived)
(org-end-of-subtree t))
  (and org-agenda-skip-comment-trees
(get-text-property p :org-comment)
(org-end-of-subtree t))
  (and (setq to (or (org-agenda-skip-eval org-agenda-skip-function-global)
    (org-agenda-skip-eval org-agenda-skip-function)))
(goto-char to))
  (org-in-src-block-p t))
      (throw :skip t))))

Can you recreate this error in an emacs -Q session with only that org
version loaded?

On Fri, Aug 5, 2016 at 3:50 AM Robert Irelan <rirelan@gmail.com> wrote:

> Trying again since it wasn't received the first time.
>
> On Tue, Aug 2, 2016 at 12:02 PM Robert Irelan <rirelan@gmail.com> wrote:
>
>> Ever since updating to 20160801, I've encountered the following error
>> whenever trying to run org-agenda-list:
>>
> --

Kaushal Modi