When you encounter this error, try grails clean. That helps in my case (the error occurs sometimes when running grails run-app from the command line, Grails 2.2.4)
| Error [localhost-startStop-1] ERROR context.GrailsContextLoader - Error initializing the application: null Message: null Line | Method ->> 41 | reload in grails.plugin.cache.ConfigLoader - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - | 193 | reloadCaches in CacheGrailsPlugin