That is because the url was not changed in the dotlrn.info file :P ( maybe Joel missed that one when taking up versions for the release).
it should be url="https://openacs.org/repository/download/apm/dotlrn-2.2.0a1";
instead of utl="https://openacs.org/repository/download/apm/dotlrn-2.1.3";
i commited the change. So feel free to update your code.
Regards,
Victor Guerra.