xupdate update fails but query using xpath succeeds?

Hello,

Im trying to execute a xupdate to change the value of an element in an 
document.

String updateXml = "<xupdate:modifications version=\"1.0\""
                        + " xmlns:xupdate=\"http://www.xmldb.org/xupdate\">"
                        + "<xupdate:update 
select=\"/domain/service[@key='PLAYOUT']/memberVariable[name='channel'] \">" 
+ "channel1"
            + "</xupdate:update>"
            + "</xupdate:modifications>";

            Collection collection = con.getCollection();
            XUpdateQueryService updateService = (XUpdateQueryService)
                collection.getService("XUpdateQueryService", "1.0");
            updateService.updateResource("PO-NI-01", updateXml);

The exception thrown is @ the server ...
1168620 [http-8080-Processor23] WARN  
org.apache.xindice.core.xupdate.XUpdateQueryResolver  - ignored exception
java.lang.NullPointerException
        at org.xmldb.xupdate.lexus.commands.UpdateCommand.execute(Unknown 
Source)
        at 
org.apache.xindice.core.xupdate.XUpdateImpl.execute(XUpdateImpl.java:116)
        at 
org.apache.xindice.core.xupdate.XUpdateQueryResolver$XUpdateQuery.execute(XUpdateQueryResolver.java:142)
        at 
org.apache.xindice.core.xupdate.XUpdateQueryResolver.query(XUpdateQueryResolver.java:84)
        at 
org.apache.xindice.core.query.QueryEngine.query(QueryEngine.java:122)
        at 
org.apache.xindice.core.Collection.queryDocument(Collection.java:1242)
        at org.apache.xindice.server.rpc.messages.Query.execute(Query.java:58)
        at 
org.apache.xindice.server.rpc.RPCMessageInterface.run(RPCMessageInterface.java:48)
        at sun.reflect.GeneratedMethodAccessor137.invoke(Unknown Source)
        at 
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at org.apache.xmlrpc.Invoker.execute(XmlRpcServer.java)
        at 
org.apache.xmlrpc.XmlRpcServer$Worker.executeInternal(XmlRpcServer.java)
        at org.apache.xmlrpc.XmlRpcServer$Worker.execute(XmlRpcServer.java)
        at org.apache.xmlrpc.XmlRpcServer.execute(XmlRpcServer.java)
        at org.apache.xmlrpc.XmlRpcServer.execute(XmlRpcServer.java)
        at 
org.apache.xindice.server.XindiceServlet.doPost(XindiceServlet.java:90)
....................

From the client it appears as if the update is successfull!  Ive tested the 
select part of the xupdate query and it returns a document segement as 
expected - I tested this with ....

Collection collection = con.getCollection();
            XPathQueryService queryService = (XPathQueryService) 
                collection.getService("XPathQueryService", "1.0");
            ResourceSet resourceSet = queryService.query(queryXml);


Any ideas on this matter are greatly appreciated, as it doesnt make sense to 
me :)

Configuration: xindice 1.1b4, tomcat 5.0.30, jdk 1.5, os RH 9.0.

Regards,
Julie.