This plugin is not compatible with Grails 2.x. You may want to have a look at http://grails.org/plugin/multi-tenant-single-db.

The plugin documentation is now hosted here: http://multi-tenant.github.com/grails-multi-tenant-core

The source code is available in github: Source code is now hosted this github repo

This is a refactoring of the original Multi-Tenant plugin to allow for more modularity and to move the development stream on to github and allow other developers to make changes and contributions in a better fashion. The initial release will match the last release of the original plugin. Future development and forks will be done in git hub and the source can be located here. Check back here for the latest status.