ClassCastException with Derby db on geronimo server

When deploying xwiki-standard.war a ClassCastException follows.Hibernate cannot resolve a placeholder.

part of logfile:
007-11-26 22:09:52,752 [DEBUG] (GeronimoLog.java:66) - resolving reference to class: com.xpn.xwiki.objects.BaseProperty
2007-11-26 22:09:52,758 [DEBUG] (GeronimoLog.java:66) - Cache: exception while getting doc xwiki:XWiki.XWikiPreferences for real
com.xpn.xwiki.XWikiException: Error number 3202 in 3: Exception while reading document XWiki.XWikiPreferences
Wrapped Exception: java.util.HashSet cannot be cast to java.lang.String
at com.xpn.xwiki.store.XWikiHibernateStore.loadXWikiDoc(XWikiHibernateStore.java:459)
at com.xpn.xwiki.store.XWikiCacheStore.loadXWikiDoc(XWikiCacheStore.java:158)
at com.xpn.xwiki.XWiki.getDocument(XWiki.java:981)
at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1015)
at com.xpn.xwiki.XWiki.getPrefsClass(XWiki.java:2266)
at com.xpn.xwiki.XWiki.initXWiki(XWiki.java:719)
at com.xpn.xwiki.XWiki.<init>(XWiki.java:611)
at com.xpn.xwiki.XWiki.getMainXWiki(XWiki.java:238)
at com.xpn.xwiki.XWiki.getXWiki(XWiki.java:397)
at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:94)
......

Wrapped Exception:

java.lang.ClassCastException: java.util.HashSet cannot be cast to java.lang.String
at org.hibernate.util.PropertiesHelper.resolvePlaceHolders(PropertiesHelper.java:88)
at org.hibernate.cfg.Configuration.buildSessionFactory(Configuration.java:1173)
at com.xpn.xwiki.store.XWikiHibernateBaseStore.initHibernate(XWikiHibernateBaseStore.java:142)
at com.xpn.xwiki.store.XWikiHibernateBaseStore.checkHibernate(XWikiHibernateBaseStore.java:464)
at com.xpn.xwiki.store.XWikiHibernateStore.loadXWikiDoc(XWikiHibernateStore.java:352)
at com.xpn.xwiki.store.XWikiCacheStore.loadXWikiDoc(XWikiCacheStore.java:158)
at com.xpn.xwiki.XWiki.getDocument(XWiki.java:981)
at com.xpn.xwiki.XWiki.getDocument(XWiki.java:1015)
at com.xpn.xwiki.XWiki.getPrefsClass(XWiki.java:2266)
at com.xpn.xwiki.XWiki.initXWiki(XWiki.java:719)
at com.xpn.xwiki.XWiki.<init>(XWiki.java:611)
at com.xpn.xwiki.XWiki.getMainXWiki(XWiki.java:238)
at com.xpn.xwiki.XWiki.getXWiki(XWiki.java:397)
at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:94)
at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:431)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:236)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1196)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:414)