task sync from webgui to outlook failed

hello,

we are using ox community edition 6.9.0.0-31.1 and oxtender 6.2.0.29.

if the create a task at the webgui, it does not appear in outlook 2003. otherwise, if i create a task in outlook, it is synced and appears in the webgui.

the tasks, we are create are simple ones with more or less content.
all other syncs, like contacts and appointments, work fine.

what could be the problem?

access.log says

Code:

PUT /ajax/tasks?action=new&folder=113&session=802905bdf14d41e38fda453994acb560 HTTP/1.0 - HTTP/1.1 200 OK (changed_adress.net/- -> 10.0.0.20:80) 0.010 sec
GET /ajax/link?action=all&session=802905bdf14d41e38fda453994acb560&folder=113&id=56&module=4 HTTP/1.0 - HTTP/1.1 200 OK (changed_adress.net/- -> 10.0.0.20:80) 0.004 sec
PROPFIND /servlet/webdav.folders HTTP/1.0 - HTTP/1.1 207 Multistatus (www.changed_adress.net/- -> 10.0.0.20:80) 0.009 sec

open-xchange.log says

Code:

May 6, 2009 10:36:26 AM com.openexchange.webdav.xml.XmlServlet doPropFind
SEVERE: doPropFind
java.lang.UnsupportedOperationException
        at com.openexchange.groupware.tasks.mapping.Alarm.getDBColumnName(Alarm.java:34)
        at com.openexchange.groupware.tasks.SQL.getFields(SQL.java:241)
        at com.openexchange.groupware.tasks.RdbTaskSearch.listModifiedTasks(RdbTaskSearch.java:120)
        at com.openexchange.groupware.tasks.TasksSQLInterfaceImpl.getModifiedTasksInFolder(TasksSQLInterfaceImpl.java:223)
        at com.openexchange.webdav.xml.TaskWriter.startWriter(TaskWriter.java:199)
        at com.openexchange.webdav.tasks.startWriter(tasks.java:214)
        at com.openexchange.webdav.xml.XmlServlet.doPropFind(XmlServlet.java:346)
        at com.openexchange.tools.webdav.WebDavServlet.service(WebDavServlet.java:159)
        at com.openexchange.tools.webdav.OXServlet.service(OXServlet.java:136)
        at com.openexchange.webdav.PermissionServlet.service(PermissionServlet.java:104)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
        at com.openexchange.ajp13.AJPv13RequestHandler.doServletService(AJPv13RequestHandler.java:575)
        at com.openexchange.ajp13.AJPv13Request.response(AJPv13Request.java:108)
        at com.openexchange.ajp13.AJPv13RequestHandler.createResponse(AJPv13RequestHandler.java:385)
        at com.openexchange.ajp13.AJPv13Connection.createResponse(AJPv13Connection.java:192)
        at com.openexchange.ajp13.AJPv13Listener.run(AJPv13Listener.java:245)
        at java.lang.Thread.run(Thread.java:636)

thanks
cornfelt