Thanks for everyone's help. We've isolated the problem on our end. You
might be affected if you have AdWords, AdSense, *and* MCC accounts.
While we whip up a fix, someone figured out this workaround:
http://groups-beta.google.com/group/adwords-api/messages/dd5d2b9f07dbd4d4,58bf2a5d05f253ed,2019b40f72eceb92,2049f98afec19591,ec9747b9057ff78a?hl=en&thread_id=d47d8ca2fdad4863&mode=thread&noheader=1&_done=%2Fgroup%2Fadwords-api%2Fbrowse_frm%2Fthread%2Fd47d8ca2fdad4863%2F2049f98afec19591%3F#doc_2049f98afec19591.
Cool!
-- Brian