Incorrect position of form object in spring controller

Today I wasted some time to find out why my spring controller method errors out even before entering into the method.
My failing method is:

	@RequestMapping(value = "/enter", method = RequestMethod.POST)
	public String enter(@ModelAttribute @Valid User user, HttpServletRequest request, ModelMap map, HttpSession session,
	BindingResult result) {
	if (result.hasErrors()) {
	logger.debug("validation error");
	map.addAttribute("error", result.getFieldError().getDefaultMessage());
	return "enter.again";
	}
	try {
	userService.create(user);
	} catch (Exception e) {
	logger.warn("User with email address \"" + user.getEmailAddress() + "\" Already Exists");
	map.addAttribute("error", "User with email address \"" + user.getEmailAddress() + "\" Already Exists");
	return "enter.again";
	}
	return "done";
	}

view raw gistfile1.java hosted with ❤ by GitHub

But I knew I am doing things right. I debugged  the application and then searched on net but could find why it is failing. Suddenly I thought is it the position of the "User" model attribute which is causing the issue. Then I changed the method as below:

	@RequestMapping(value = "/enter", method = RequestMethod.POST)
	public String enter(HttpServletRequest request, ModelMap map, HttpSession session,
	@ModelAttribute @Valid User user, BindingResult result) {
	if (result.hasErrors()) {
	logger.debug("validation error");
	map.addAttribute("error", result.getFieldError().getDefaultMessage());
	return "enter.again";
	}
	try {
	userService.create(user);
	} catch (Exception e) {
	logger.warn("User with email address \"" + user.getEmailAddress() + "\" Already Exists");
	map.addAttribute("error", "User with email address \"" + user.getEmailAddress() + "\" Already Exists");
	return "enter.again";
	}
	return "done";
	}

view raw gistfile1.java hosted with ❤ by GitHub

Notice that I moved the method argument "@ModelAttribute @Valid User user" from first to second last. And Voila!! it worked.

FYI: I am using Spring 3.2.