Read on the last page that several people have encountered this error with AO3 but managed a work around by manipulating the "is adult=" line by either turning it off (adding # in front) or inputing "false".
Neither one worked.
I had no problems when I just login to the same story with my web browser (Chrome/MacOSX) so not quite sure what's going on.
Been trying all night with no success. Any ideas?
Thanks!