RYTHM not working deployed on GAE server, works on local GAE server. (1)

Question

I configured Rythm to:

RythmEngine engine = null;
Map<String, Object> conf = new HashMap<String, Object>();
conf.put("engine.file_write", false);
engine = new RythmEngine(conf);
String body = engine.render("hello @who!", "kitty");
resp.getWriter().println("{ \"name\": \""+body+"\" }");

Works great on the local GAE server, but the i deploy it on the google server, i get the file write error. I assume the configuration "engine.file_write" is not changed to false or changed to default. Why is this happening? Is there a solution?