In the afternoon, a member of MF Global's finance team in Chicago sends out an email, according to which the daily summary of the segregated customer account for Friday shows a $952 million deficit. The operating assumption at this stage is that the figure is the result of an accounting error. Members of the finance team, regulators (some of whom are now on site in Chicago), and, ultimately, even a team from prospective acquirer Interactive Brokers work feverishly through the afternoon and the evening to try to resolve the "error." Monday, Oct. 31: MF Global files for bankruptcy Between 12 a.m. and 1 a.m., O'Brien hands Christine Serwinski, CFO of MF Global North America, a document that traces the deficit to three types of transactions: All told, the transactions add up to $900 million. Serwinski immediately understands that the deficit is genuine and no accounting error. At 1 a.m., O'Brien and Serwinski tell the CME Group ( NYS: CME ) there is a genuine deficit in segregated customer funds.