After a build runs, it tries to do a campfire notification and fails as follows. Downgraded Jenkins back to 1.423 and all is well.

FATAL: com.gargoylesoftware.htmlunit.WebClient.setCookiesEnabled(Z)V
java.lang.NoSuchMethodError: com.gargoylesoftware.htmlunit.WebClient.setCookiesEnabled(Z)V
at hudson.plugins.campfire.Campfire.<init>(Campfire.java:51)
at hudson.plugins.campfire.CampfireNotifier.initialize(CampfireNotifier.java:62)
at hudson.plugins.campfire.CampfireNotifier.initialize(CampfireNotifier.java:58)
at hudson.plugins.campfire.CampfireNotifier.checkCampfireConnection(CampfireNotifier.java:53)
at hudson.plugins.campfire.CampfireNotifier.publish(CampfireNotifier.java:42)
at hudson.plugins.campfire.CampfireNotifier.perform(CampfireNotifier.java:80)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:682)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:657)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:635)
at hudson.model.Build$RunnerImpl.post2(Build.java:161)
at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:604)
at hudson.model.Run.run(Run.java:1400)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:175)