LOD extension fails to load in RapidMiner 6

Dear all,

We wanted to test our Linked Open Data extension if it is compatible with RapidMiner 6. The extension can be successfully installed from the marketplace, but after RapidMiner restarts the extension cannot be loaded. The log output is:

WARNING: Plugin initializer com.rapidminer.PluginInitTemplate.initPlugin of Plugin LOD caused an error: null 
java.lang.reflect.InvocationTargetException
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
	at java.lang.reflect.Method.invoke(Unknown Source)
	at com.rapidminer.tools.plugin.Plugin.callInitMethod(Plugin.java:897)
	at com.rapidminer.tools.plugin.Plugin.callPluginInitMethods(Plugin.java:868)
	at com.rapidminer.tools.plugin.Plugin.initPlugins(Plugin.java:847)
	at com.rapidminer.tools.plugin.Plugin.initAll(Plugin.java:988)
	at com.rapidminer.RapidMiner.init(RapidMiner.java:636)
	at com.rapidminer.RapidMiner.init(RapidMiner.java:584)
	at com.rapidminer.gui.RapidMinerGUI.run(RapidMinerGUI.java:304)
	at com.rapidminer.gui.RapidMinerGUI.launch(RapidMinerGUI.java:792)
	at com.rapidminer.gui.RapidMinerGUI.main(RapidMinerGUI.java:773)
Caused by: java.lang.NoClassDefFoundError: com/rapidminer/tools/config/gui/ConfigurationPanel
	at com.rapidminer.PluginInitTemplate.initPlugin(PluginInitTemplate.java:27)
	... 13 more
Caused by: java.lang.ClassNotFoundException: com.rapidminer.tools.config.gui.ConfigurationPanel
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.net.URLClassLoader$1.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(Unknown Source)
	at com.rapidminer.tools.plugin.PluginClassLoader.loadClass(PluginClassLoader.java:90)
	at java.lang.ClassLoader.loadClass(Unknown Source)
	... 14 more

The output shows that the class com.rapidminer.tools.config.gui.ConfigurationPanel cannot be found, which is used in the extension for generating custom configurators ( see "How to Extend RapidMiner 5" - chapter 8.2). We checked the rapidminer.jar of RapidMiner 6, and indeed the class com.rapidminer.tools.config.gui.ConfigurationPanel is missing.

We are confused why is the class missing in RapidMiner 6, and how can we resolve this issue?

Any help or tips are appreciated,

Petar