We have met this strange issue before. It turned out that Internet Explorer fires readystatechange
twice with readyState
1 and the second execution of the handler causes the error. I assume that this could also be reproduced outside of the Kendo UI Upload widget environment with a standard XMLHttpRequest. Nevertheless as a workaround for the the current case you could name the executed handler and unbind it after the first execution.
xhr = e.XMLHttpRequest;
(xhr.readyState == 1
/* OPENED */
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