I've find the solution of this probelm.
In order to solve this problem, we need to use this version of task complete method:
BlockingTaskOperationResponseHandler responseHandler = new BlockingTaskOperationResponseHandler();
Map<String, Object> taskVariables = new HashMap<String, Object>();
taskVariables.put(new String("o_validationResult"),Boolean.valueOf(true));
ContentData contentData = null;
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream out;
try {
out = new ObjectOutputStream(bos);
out.writeObject(taskVariables);
out.close();
contentData = new ContentData();
contentData.setContent(bos.toByteArray());
contentData.setAccessType(AccessType.Inline);
} catch (IOException ioe) {
ioe.printStackTrace();
}
client.complete(aTaskId, aOwnerId, contentData, responseHandler);
With this code the task completion with a map of variables must done successfully.