Even though RFC 6265's cookie-value's cookie-octet definition says that whitespace characters are not allowed (see http://tools.ietf.org/html/rfc6265), there are non-compliant web sites that send cookie values with newlines.  cookielib.LWPCookieJar will save the bad value in a cookie file, but when it tries to load it, it probably is only splitting by newlines, so it crashes on the invalid line.  The easiest thing would probably be to just ignore cookies that have values with a newline.  (Note: I'm using Python 2.5, so this might have been fixed in a later version.)