Evaluation on export has stopped working, org-export-blocks hook was culprit?

[Herbert Sitz <hesitz@gmail.com>]

I had a system that was working fine, but it seems to have stopped processing
babel source blocks on export.  I've switched between Org 7.4 and 7.7 on Win32
Emacs 23.1 and both have the problem.  

As I was writing this up I discovered that the problem was caused by a line I
had added to my .emacs.  This line was preventing any evaluation of source
blocks at all:
--------------------------------------------
 '(org-export-blocks (quote ((comment org-export-blocks-format-comment nil)
(ditaa org-export-blocks-format-ditaa nil) (dot org-export-blocks-format-dot
nil))))
--------------------------------------------

I had innocently been testing out export of comments with org-export-blocks hook
and I had forgotten I put that in .emacs some days ago.  

It seems to have prevented any processing of my source blocks on export.  That
is the export of the block simply exports the code between begin_src and
end_src, regardless of the value of :exports option (both, none, results, code).
 And, of course, the code in the source block was not getting evaluated.

Don't know if this is a known problem or not.  

Thanks,

Herb