[Users] deploying ovirt-engine from src

After following the steps in http://www.ovirt.org/Building_oVirt_engine, I met some problems in deploying it. Here's the status while I visit http://localhost:8700/webadmin/webadmin/WebAdmin.html 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 org.ovirt.engine.ui.frontend.server.gwt.GwtCachingFilter.doFilter(GwtCachingFilter.java:132) *root cause* java.lang.NoClassDefFoundError: Could not initialize class org.ovirt.engine.ui.frontend.server.gwt.plugin.PluginDataManager$Holder org.ovirt.engine.ui.frontend.server.gwt.plugin.PluginDataManager.getInstance(PluginDataManager.java:74) org.ovirt.engine.ui.frontend.server.gwt.WebAdminHostPageServlet.getPluginData(WebAdminHostPageServlet.java:85) org.ovirt.engine.ui.frontend.server.gwt.WebAdminHostPageServlet.doGet(WebAdminHostPageServlet.java:53) javax.servlet.http.HttpServlet.service(HttpServlet.java:734) javax.servlet.http.HttpServlet.service(HttpServlet.java:847) org.ovirt.engine.ui.frontend.server.gwt.GwtCachingFilter.doFilter(GwtCachingFilter.java:132) *note* *The full stack trace of the root cause is available in the JBoss Web/7.0.13.Final logs.* ------------------------------ JBoss Web/7.0.13.Final What does it mean? And What should I do next? Thanks!!