I am having trouble with some javascript. The code snippet below creates a simple post request however it always throws an NS_Error_failure exception (details at the bottom of the page). Can anyone tell me whats wrong with this code?

window.onload = function () {



    alert('0');

    try {

        var url = Some URL;

        var request = CreateHttpRequest();

        if (request) {

            alert('1');

            request.open(POST, url, false);

            request.setRequestHeader(Content-type, application/x-www-form-urlencoded);

            alert('2');

            request.send('');

            alert('3');

        }

    }

    catch (err) {

        alert(err);

    }

}

    [Exception... Component returned failure code: 0x80004005 (NS_ERROR_FAILURE)

     nsresult: 0x80004005 (NS_ERROR_FAILURE)  

     location: JS frame :: file:///C:/Users/Ben/Desktop/test.html :: <TOP_LEVEL> :: line 44  data: no]