SC-WIN32-STATUS 1236 (in web log)

I see this error code (as the sc-win32-status) occasionally in my IIS log. I
have a page that gets hit 100's or 1000's of times a day on my site and
normally it works fine. Once in a while it will have an entry with this
sc-win32-status code, but the HTTP status code is 200 (OK). Typically thes
entries will show much longer than normal processing time in the web log.
The page typically responds in less than 1/2 second, but when it gets a 1236
it may run 15 seconds and often 30 or more.

I know the help text for this message is "The network connection was aborted
by the local system." But I don't understand what that means ? Is IIS
timing the request out ? If so why the variability in processing time and why
are there no corresponding entries in the windows event log ? Could this be
related to the user closing his browser while the server was still processing
the request ?