Lucene Plugin broken

HTTP Status 500 -

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception
com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:121)

root cause

java.lang.NoClassDefFoundError: org/apache/lucene/index/IndexReader
java.lang.Class.forName0(Native Method)
java.lang.Class.forName(Class.java:164)
com.xpn.xwiki.plugin.XWikiPluginManager.addPlugin(XWikiPluginManager.java:66)
com.xpn.xwiki.plugin.XWikiPluginManager.addPlugins(XWikiPluginManager.java:97)
com.xpn.xwiki.XWiki.preparePlugins(XWiki.java:709)
com.xpn.xwiki.XWiki.initXWiki(XWiki.java:663)
com.xpn.xwiki.XWiki.<init>(XWiki.java:566)
com.xpn.xwiki.XWiki.getMainXWiki(XWiki.java:281)
com.xpn.xwiki.XWiki.getXWiki(XWiki.java:382)
com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:96)
org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
com.xpn.xwiki.web.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:121)

note The full stack trace of the root cause is available in the Apache Tomcat/5.5.20 logs.