Hey there (again...), after two days of use, a co-worker found a problem with the register-page for new accounts; the site loads with a 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.ActionFilter.doFilter(ActionFilter.java:120) org.xwiki.wysiwyg.server.filter.ConversionFilter.doFilter(ConversionFilter.java:144) com.xpn.xwiki.plugin.webdav.XWikiDavFilter.doFilter(XWikiDavFilter.java:66) org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208) org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:111) root cause java.lang.NoClassDefFoundError: Could not initialize class com.xpn.xwiki.web.RegisterAction sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57) sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) java.lang.reflect.Constructor.newInstance(Constructor.java:532) java.lang.Class.newInstance0(Class.java:374) java.lang.Class.newInstance(Class.java:327) org.apache.struts.util.RequestUtils.applicationInstance(RequestUtils.java:143) org.apache.struts.action.RequestProcessor.processActionCreate(RequestProcessor.java:292) org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:230) 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:617) javax.servlet.http.HttpServlet.service(HttpServlet.java:717) com.xpn.xwiki.web.ActionFilter.doFilter(ActionFilter.java:120) org.xwiki.wysiwyg.server.filter.ConversionFilter.doFilter(ConversionFilter.java:144) com.xpn.xwiki.plugin.webdav.XWikiDavFilter.doFilter(XWikiDavFilter.java:66) org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208) org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:111) note The full stack trace of the root cause is available in the Apache Tomcat/6.0.35 logs./ unfortunately i'm not familiar with the whole java-stuff, so maybe you can help me? Regards, Eric -- View this message in context: http://xwiki.475771.n2.nabble.com/Upgrade-problem-xwiki-4-4-to-5-1-tp7587221... Sent from the XWiki- Users mailing list archive at Nabble.com.