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Data for a POST Request Is Not Downloaded Completely
http://www.vistaarticles.com/articles/159/1/Data-for-a-POST-Request-Is-Not-Downloaded-Completely
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Published on 11/23/2006
 
When Internet Explorer makes a POST request for data with a MIME type that is handled by a custom ActiveX control, Internet Explorer stops downloading the data after the first portion is received.

Data for a POST Request Is Not Downloaded Completely

To work around this problem, you can either use a GET request, or you can make a POST request for the HTML file that hosts the ActiveX control by using the OBJECT tag.

Details: http://support.microsoft.com/kb/310388/en-us?spid=2073&sid=global