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I have a mojoportal CMS installation on an IIS7 server where users are reporting problems downloading a pdf file. It always downloads fine for me and most others, either displaying in browser or in Adobe Reader.

Using logparser to query the IIS logs, all the responses are status 200 (OK) or 304 (Not modified), but the bytes sent vary quite a bit. Sometimes zero, some 211, some about half the full file size of 27059, and lots in between. Plenty show the full size of 27059.

Do these other entries for smaller byte counts represent errors of some kind, correlating with the problems reported? Is this likely to be a browser/client issue or a server side problem?

If there is any other info that would be helpful let me know. This is a shared hosting server though so I am somewhat limited in what I can dig into on the server.

*edit: I have noticed that the log entries with smaller byte counts are in a series of entries for the same client IPs, so I guess the browser is doing something where it gets the file in chunks over multiple requests. Summing the bytes by client still doesn't result in consistent total bytes transfered per client.

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Found this thread: forums.iis.net/t/1161071.aspx which indicates this is an IIS defect on Windows Server 2008 R2 related to multiple byte-range requests. I am testing the hotfix at support.microsoft.com/kb/979543 on another machine. –  Pat James Apr 14 '10 at 15:17
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up vote 0 down vote accepted

I implemented the hotfix at http://support.microsoft.com/kb/979543 on a VPS server I run and it has resolved the problem. Now to see how long my hosting company takes to implement the hotfix on their shared IIS server.

It is a tricky one to diagnose since it depends on the version of the Adobe Reader browser plugin installed on the client.

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