On button click in Extjs 4.0.2

on button two Ajax request send to ".cfm" page, for two times button click it's working fine but in third time when i 开发者_JS百科button press the Error "an ajax response error has occured.

function ViewOpenPoll() {
    Ext.Ajax.request({
        url:QVisibleLink,
        // ON button click function viewpoll invoke
        // and the given url in ajax request has send.
        disableCaching: true,
        success: function(response) {
            obj = Ext.decode(response.responseText);
        }
    });
}

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Access the .cfm page directly with your browser 3 times in a row. Does it work?