By design, the ASP.NET AJAX Framework cancels the ongoing AJAX request if you try to initiate another one prior to receiving the response from the first one.
To change this behavior, you can set the RequestQueueSize property to a value greater than zero, which enables the queueing mechanism of RadAjax,
and will allow you to complete the ongoing request and then initiate the pending requests in the control queue.
If the queue is full (queue size equals RequestQueueSize), an attempt for new AJAX requests will be discarded.
The default value is 0 (queueing disabled).