After installing the add-on, when trying to open configuration pages, add-on administration or content tools, i get: Error occurred during template rendering: Invocation of method 'getConfluenceResourceTags' in class com.atlassian.confluence.setup.velocity.VelocityFriendlyPageBuilderService threw exception java.lang.NoClassDefFoundError: Could not initialize class com.atlassian.upm.osgi.impl.Versions at /decorators/includes/header.vm[line 88, column 24]. Contact your administrator for assistance.
Not wearing my "happy-face" at the moment!