http://www.mail-archive.com/emacs-orgmode@gnu.org/msg21593.html

im trying to set up ditaa on my cygwin/windows7 machine and encountered the
very same problem as described in the above mentioned mail, i.e. the error
"jar not accessible".
i tried to fix it by hacking org-exp-blocks, but it does not seem to make
any difference. when i check the *Messages* buffer, the path to ditaa.jar
is unchanged.
If anyone has this one figured out, i would appreciate your help.