If you run grails upgrade on an application that has several plugins installed, it will do so fine. However when you run-app you get obscure JDOM/XPath errors as the plugins have out of date plugin.xml data files. All plugins have to be manually upgraded and rebuilt with RC2 and re-installed to workaround this, which is painful on non-trivial projects especially if you dont have plugin source easily to hand. Possible remedies: 1) Make upgrade detect plugins and warn user that upgrade will require them all to be rebuilt 2) Make upgrade update the plugin.xml files (perhaps fragile) 3) Don't break the XML in this way, make it backwards compatible I favour 3 if at all possible.