I upgraded JIRA from 5.x to latest 7.x. I see this error. any help on what is the resolution?
2016-06-03 18:31:44,844 JIRA-Bootstrap ERROR [c.a.plugin.manager.DefaultPluginManager] There was an error loading the descriptor 'Create a new issue or add a comment to an existing issue' of plugin 'com.atlassian.jira.jira-mail-plugin'. Disabling. java.lang.ClassCastException: com.atlassian.jira.plugins.mail.extensions.ProjectRequiredMessageHandlerValidator cannot be cast to com.atlassian.jira.plugins.mail.extensions.MessageHandlerValidator at com.atlassian.jira.plugins.mail.extensions.MessageHandlerModuleDescriptor.enabled(MessageHandlerModuleDescriptor.java:58) at com.atlassian.plugin.manager.DefaultPluginManager.notifyModuleEnabled(DefaultPluginManager.java:1991) at com.atlassian.plugin.manager.DefaultPluginManager.enableConfiguredPluginModule(DefaultPluginManager.java:1738) at com.atlassian.plugin.manager.DefaultPluginManager.enableConfiguredPluginModules(DefaultPluginManager.java:1715) at com.atlassian.plugin.manager.DefaultPluginManager.enableDependentPlugins(DefaultPluginManager.java:1227) at com.atlassian.plugin.manager.DefaultPluginManager.addPlugins(DefaultPluginManager.java:1188) at com.atlassian.jira.plugin.JiraPluginManager.addPlugins(JiraPluginManager.java:150) at com.atlassian.plugin.manager.DefaultPluginManager.earlyStartup(DefaultPluginManager.java:573) at com.atlassian.jira.plugin.JiraPluginManager.earlyStartup(JiraPluginManager.java:118) at com.atlassian.jira.ComponentManager$PluginSystem.earlyStartup(ComponentManager.java:610) at com.atlassian.jira.ComponentManager.quickStart(ComponentManager.java:188) at com.atlassian.jira.ComponentManager.start(ComponentManager.java:157) at com.atlassian.jira.upgrade.PluginSystemLauncher.start(PluginSystemLauncher.java:43) at com.atlassian.jira.startup.DefaultJiraLauncher.lambda$postDbLaunch$2(DefaultJiraLauncher.java:146) at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrEnqueue(DatabaseConfigurationManagerImpl.java:298) at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrWhenDatabaseActivated(DatabaseConfigurationManagerImpl.java:194) at com.atlassian.jira.startup.DefaultJiraLauncher.postDbLaunch(DefaultJiraLauncher.java:137) at com.atlassian.jira.startup.DefaultJiraLauncher.lambda$start$0(DefaultJiraLauncher.java:103) at com.atlassian.jira.util.devspeed.JiraDevSpeedTimer.run(JiraDevSpeedTimer.java:31) at com.atlassian.jira.startup.DefaultJiraLauncher.start(DefaultJiraLauncher.java:101) at com.atlassian.jira.startup.LauncherContextListener.initSlowStuff(LauncherContextListener.java:115) at java.lang.Thread.run(Thread.java:745)
