Why does urlgrabber reports "Connection Reset by Peer" when connecting to third party repositories ?

Issue

• There is a Red Hat Enterprise Linux 5 machine which is configured to connect to the VMWare tools repository on packages.vmware.com that are no longer able to update.
• All of the Red Hat Enterprise Linux 6 machines are able to connect without a problem.
• Running yum update on the Red Hat Enterprise Linux 5 systems give the error "http://packages.vmware.com/tools/esx/5.5latest/rhel5/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 502: Connection reset by peer", and running urlgrabber on that URL gives the following output:

urlgrabber http://packages.vmware.com/tools/esx/5.5latest/rhel5/x86_64/repodata/repomd.xml
Traceback (most recent call last):
  File "/usr/bin/urlgrabber", line 124, in ?
    main()
  File "/usr/bin/urlgrabber", line 120, in main
    filename = urlgrab(url,filename=file,**kwargs)
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 602, in urlgrab
    return default_grabber.urlgrab(url, filename, **kwargs)
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 936, in urlgrab
    return self._retry(opts, retryfunc, url, filename)
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 854, in _retry
    r = apply(func, (opts,) + args, {})
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 922, in retryfunc
    fo = URLGrabberFileObject(url, filename, opts)
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1010, in __init__
    self._do_open()
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1093, in _do_open
    fo, hdr = self._make_request(req, opener)
  File "/usr/lib/python2.4/site-packages/urlgrabber/grabber.py", line 1216, in _make_request
    raise new_e
urlgrabber.grabber.URLGrabError: [Errno 14] HTTP Error 502: Connection reset by peer

• Red Hat Enterprise Linux 5.11 machines HTTP(S) requests are proxied through Websense Proxy, but again it's the same environment as the Red Hat Enterprise Linux 6 systems that work just fine.