Upload/Replace process XML via Jazz API

Hello All,
I would like to replace an existing process XML with a modified version from the file system.

I tried this with the follwing code.
private static void uploadXMLSource(IProjectArea ip,IProgressMonitor sPm) throws TeamRepositoryException,
        UnsupportedEncodingException {
             
                ITeamRepository tr = (ITeamRepository) ip.getOrigin();
                Map <String, Object> pd = ip.getProcessData();
                IContent content = (IContent) pd.get(ProcessContentKeys.PROCESS_SPECIFICATION_KEY);
               
                if (content != null) {
                    System.out.println("Modify: " + content);
                   
                    String newProcess = "c:/temp/processXML_JKE Banking (Change Management).xml";
                    //String newProcessString;
                    try {
                    String newProcessString = readFile(newProcess);
                    System.out.println("ProcessString: " + newProcessString);
                    IContent newContent = createContentFromString(tr, newProcessString, sPm);
                    System.out.println("new content: " + newContent);
                    pd.put(ProcessContentKeys.PROCESS_SPECIFICATION_KEY, newContent);
                   
                    IProcessItemService processItemService = (IProcessItemService) tr
                            .getClientLibrary(IProcessItemService.class);
                    processItemService.save(ip, sPm);
                    } catch (IOException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                   
                   
But as result I just have the following exception:
Exception in thread "main" com.ibm.team.repository.common.internal.ImmutablePropertyException
    at com.ibm.team.repository.common.internal.util.ItemUtil$ProtectAdapter.notifyChanged(ItemUtil.java:2159)
    at org.eclipse.emf.common.notify.impl.BasicNotifierImpl.eNotify(BasicNotifierImpl.java:374)
    at org.eclipse.emf.common.notify.impl.NotificationImpl.dispatch(NotificationImpl.java:1027)
....

Could you please support me resolving this problem.
Many thanks,
Christine