Many people think Erin Callan, then chief financial officer of Lehman Brothers, made a big mistake a few months ago when she took a call from David Einhorn, a hedge fund manager whose fund had taken a big short stake in the Wall Street investment bank.

The reason? Ms Callan fumbled some of her responses on Lehman's asset valuations. When Mr Einhorn went public with the conversation, it only served to fuel market jitters about the bank's solidity.