Unable to load plugin TranslatorPlugin

Error while installing a Plugin.

How to reproduce:
Go to Spark -> Plugins -> Available Plugins -> Install a plugin

It appears the following error. After restarting Spark everything is ok.
Apr 12, 2007 6:50:49 PM org.jivesoftware.spark.util.log.Log error
SEVERE: Unable to load plugin org.jivesoftware.spark.translator.TranslatorPlugin.
java.lang.ClassNotFoundException: org.jivesoftware.spark.translator.TranslatorPlugin
at java.net.URLClassLoader$1.run(URLClassLoader.java:200)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at org.jivesoftware.spark.PluginManager.loadPublicPlugin(PluginManager.java:260)
at org.jivesoftware.spark.PluginManager.addPlugin(PluginManager.java:549)
at org.jivesoftware.sparkimpl.plugin.viewer.PluginViewer$4.run(PluginViewer.java:331)
at java.lang.Thread.run(Thread.java:619)