I installed a few days the new version of moodle (Moodle + 2.1.1 (Build: 20110921). I tried to install wiris 2.3.2 http://moodle.org/plugins/pluginversion.php?id=31 declared compatible with the 2.1 version and not with the 2.2.1 +.
But nothing happens.
You should really do a downgrade (then reinstall everything, 256 courses about 1200 users with enrolment), fellow in mathematics need this plugin to reuse material prepared earlier.