When looking at http://www.open-mpi.org/community/lists/devel/2005/12/0573.php for example, the "previous message" link points to http://www.open-mpi.org/mailman/private.cgi/devel/2005/11/0572.php which is inaccessible without a password.
This seems to be some mailing list configuration error, as the real previous message may be found by browsing the overview of the previous month, at http://www.open-mpi.org/community/lists/devel/2005/11/0572.php Links crossing months seem all to exhibit this behavior. Cheers, Ralf