Confluence Doesn't Start Due to 'Duplicate plugin found'


After recently installing a plugin either by placing the jar file in <CONFLUENCE_INSTALL>/confluence/WEB-INF/lib directory or via the Administration > Plugins page, confluence fails to start up with the following in the atlassian-confluence.log file:

2010-03-27 12:34:16,237 ERROR [main] [atlassian.confluence.event.ConfluenceEventManager] publishEvent An exception was encountered while processing the event:[source=com.atlassian.confluence.upgrade.impl.DefaultUpgradeManager@56be1a11]
java.lang.RuntimeException: Error initialising plugin manager: Duplicate plugin found (installed version is the same or older) and could not be unloaded: 'com.pantero.confluence.plugins.testplans'
	at com.atlassian.confluence.plugin.ConfluencePluginManager.processConfluenceReadyEvent(
	at com.atlassian.confluence.plugin.ConfluencePluginManager.onApplicationEvent(
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(
	at java.lang.reflect.Method.invoke(
	at $Proxy8.publishEvent(Unknown Source)
	at com.atlassian.confluence.upgrade.impl.DefaultUpgradeManager.upgrade(
Caused by: com.atlassian.plugin.PluginParseException: Duplicate plugin found (installed version is the same or older) and could not be unloaded: 'com.pantero.confluence.plugins.testplans'
	at com.atlassian.plugin.manager.DefaultPluginManager.addPlugins(
	at com.atlassian.plugin.manager.DefaultPluginManager.init(
	at com.atlassian.confluence.plugin.ConfluencePluginManager.init(
	at com.atlassian.confluence.plugin.ConfluencePluginManager.processConfluenceReadyEvent(
	... 46 more
Caused by: com.atlassian.plugin.PluginException: Plugin is not uninstallable: com.pantero.confluence.plugins.testplans
	at com.atlassian.plugin.manager.DefaultPluginManager.ensurePluginAndLoaderSupportsUninstall(
	at com.atlassian.plugin.manager.DefaultPluginManager.unloadPlugin(
	at com.atlassian.plugin.manager.DefaultPluginManager.uninstall(
	at com.atlassian.plugin.manager.DefaultPluginManager.updatePlugin(
	at com.atlassian.plugin.manager.DefaultPluginManager.addPlugins(
	... 49 more


A similar issue was discovered at Confluence Doesn't Start Due to 'Duplicate plugin found', however this is not considered a bug as plugins in Confluence should not be installed via the classpath (i.e. put in the <CONFLUENCE_INSTALL>/confluence/WEB-INF/lib directory). They should be only installed via the Administration >> Plugins page within the Confluence Administration.

When confluence starts up it loads the classpath plugin first and then discovers that there is a newer version of the plugin in the database. In order to install the new version it first needs to uninstall the old one, but because it is a 'classpath' plugin it cannot be uninstalled hence the exception.


Remove the plugin from the <CONFLUENCE_INSTALL>/confluence/WEB-INF/lib directory and restart Confluence.

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