Problem with jQuery.ajax with 'delete' method in ie

I have a page where the user can edit various content using buttons and selects that trigger ajax calls. In particular, one action causes a url to be called remotely, with some data and a 'put' request, which (as i'm using a restful rails backend) triggers my update action. I also have a delete button which calls the same url but with a 'delete' request. The 'update' ajax call works in all browsers but the 'delete' one doesn't work in IE. I've got a vague memory of encountering something like this before...can anyone shed any light? here's my ajax calls:

//update action - works in all browsers
jQuery.ajax({
  async:true, 
  data:data, 
  dataType:'script', 
  type:'put', 
  url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId,
  success: function(msg){ 
    initializeQuizQuestions();
    setPublishButtonStatus();
  }
});  



//delete action - fails in ie
  function deleteQuizQuestion(quizQuestionId, quizId){
    //send ajax call to back end to change the difficulty of the quiz question
    //back end will then refresh the relevant parts of the page (progress bars, flashes, quiz status)
    jQuery.ajax({
      async:true, 
      dataType:'script', 
      type:'delete', 
      url:"/quizzes/"+quizId+"/quiz_questions/"+quizQuestionId,
      success: function(msg){ 
        alert("success");
        initializeQuizQuestions();
        setSelectStatus(quizQuestionId, true);
        jQuery("tr[id*='quiz_question_"+quizQuestionId+"']").removeClass('selected');        
      },
      error: function(msg){
        alert("error:" + msg);
      }
    });     
  }

I put the alerts in success and error in the delete ajax just to see what happens, and the 'error' part of the ajax call is triggered, but WITH NO CALL BEING MADE TO THE BACK END (i know this by watching my back end server logs). So, it fails before it even makes the call. I can't work out why - the 'msg' i get back from the error block is blank.

Any ideas anyone