Justin logged a bug here and I encountered the same issue: https://issues.apache.org/jira/browse/FLEX-35271
At first glance this seems like a real quick fix, just delete the two lines from : if (contentData) { element.setRequestHeader('Content-length', contentData.length.toString()); element.setRequestHeader('Connection', 'close'); element.send(contentData); } else { element.send(); } changing to: if (contentData) { element.send(contentData); } else { element.send(); } or possibly even something like: element.send(contentData || ""); I just thought I would double-check if anyone knew why these headers were included originally. Even if it was permitted (it seems clear that it is not), I don't think that content-length would always be correct byte count in the above case if the string was utf8...because the string length can be different to its byte length. If I hear nothing or if there are no objections, I will make the change above. regards, Greg