Probable cause of winbot's recent bootstrap errors

gistfile1.txt

Python 2.7.8 (default, Oct 20 2014, 15:05:19) 
[GCC 4.9.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import urllib
>>> r = urllib.urlopen('https://pypi.python.org/packages/source/z/zc.buildout/zc.buildout-2.3.1.tar.gz')
>>> d = r.read()
>>> len(d)
292209
>>> r = urllib.urlopen('https://pypi.python.org/packages/source/z/zc.buildout/zc.buildout-2.3.1.tar.gz#md5=cbf008369ca28814ed8051084622fba8')
>>> d = r.read()
>>> len(d)
1059
>>> d
'<?xml version="1.0" encoding="UTF-8"?>\n<Error><Code>SignatureDoesNotMatch</Code><Message>The request signature we calculated does not match the signature you provided. Check your key and signing method.</Message><AWSAccessKeyId>AKIAJKIWYRSQOM4QFZ3Q</AWSAccessKeyId><StringToSign>GET\n\n\nTue, 19 May 2015 06:20:43 GMT\n/pypi-files/source/z/zc.buildout/zc.buildout-2.3.1.tar.gz#md5=cbf008369ca28814ed8051084622fba8</StringToSign><SignatureProvided>aZJf/byXZR3yuyN+Xpc0LH6WvUQ=</SignatureProvided><StringToSignBytes>47 45 54 0a 0a 0a 54 75 65 2c 20 31 39 20 4d 61 79 20 32 30 31 35 20 30 36 3a 32 30 3a 34 33 20 47 4d 54 0a 2f 70 79 70 69 2d 66 69 6c 65 73 2f 73 6f 75 72 63 65 2f 7a 2f 7a 63 2e 62 75 69 6c 64 6f 75 74 2f 7a 63 2e 62 75 69 6c 64 6f 75 74 2d 32 2e 33 2e 31 2e 74 61 72 2e 67 7a 23 6d 64 35 3d 63 62 66 30 30 38 33 36 39 63 61 32 38 38 31 34 65 64 38 30 35 31 30 38 34 36 32 32 66 62 61 38</StringToSignBytes><RequestId>197CFF63F85307C7</RequestId><HostId>VpkNKJ+uGJho5tOwGs71KQiyujsj9qFKDfwTaUntDUaO/NJhIYBLhyYc7TAvZjXSOTglP6ftTGo=</HostId></Error>'
>>> r.code
403