Symptoms

Confluence does not enable plugins. The following error appears in the atlassian-confluence.log for example when the Team Calendars for Confluence couldn't be enabled due the error but can happen to any other plugin as well.

[atlassian.plugin.manager.DefaultPluginManager] enableConfiguredPluginModule There was an error loading the descriptor 'Upcoming events in mail summary' of plugin 'com.atlassian.confluence.extra.team-calendars'. Disabling.
 -- referer: xxxxxxxx | url: /rest/plugins/1.0/com.atlassian.confluence.extra.team-calendars-key | userName: xxxxxx
java.lang.RuntimeException: Unable to enable web fragment

Cause

1) This can occur due to the JRE or JDK being corrupted or using a rather old version.

2) Can also occur due to the old version of the plugin.

Resolution

For cause 1:

1) Reinstall the latest supported JDK for the current confluence version. See the supported platforms for your current confluence version.

2) Remove the plugin cache folders and restart the application.

3) Try to enable the plugin(s) again.

For cause 2:

1) Remove the old plugin version

2) Install the latest supported version of the plugin to your confluence version. See the plugin version history on market place for this information.

3) Try to enable the plugin(s) again.