[jQuery] jquery.ajax POST is getting a 400 error intermittently

[jq-rav]

I am using jQuery ajax, served up on AIX, IBM HTTP Server and
Websphere Application server

When making a jQuery.ajax type:'POST', sometimes the reponse is:  HTTP/
1.1 400. This is not happening consistently. I see the 400 status code
in the web server logs.
Has anybody else run into this issue before?

Here is the jquery ajax call code

$.ajax({
        url: url,
        type: 'POST',
        data: {
                client: $('#txt1').val(),
                trigger: 'reload',
                product:product
    },
           dataType: 'xml',
        async: false,
        timeout: 10000,
        success: function(responseXML){
                parseAjaxoutput(responseXML);
        }

});


'#txt1' is an input type hidden element or a select box.


Appreciate your help.