Are you experiencing the following error in Confluence while trying to install a plugin?

org.apache.velocity.exception.MethodInvocationException: Invocation of method 'isModuleEnabled' in class com.atlassian.confluence.admin.actions.plugins.ManagePluginsAction threw exception java.lang.IllegalArgumentException: Invalid complete key specified: null @ /admin/plugins.vm[109,42]

Everything else is working just fine though right? After you hit your head once or twice verify that you are using the correct JDK and that you've compiled your plugin (if it's a custom plugin) using also the correct JDK. My conlfuence instance (2.8.0) was running just find, but was throwing this error until I moved to 1.5.0_14.