NEW YORK (Reuters) - Credit Suisse Group Inc faces a potential $2 billion of exposure over fraud that occurred a decade ago at National Century Financial Enterprises, a result of a federal judge's determination on how to apportion responsibility. Friday's decision by U.S. District Judge James Graham could expose the Swiss bank to hundreds of millions of dollars of added liability over the activities of Lance Poulsen, who co-founded National Century in 1990 and was its chief executive. He is now serving a 30-year prison term and is presumed insolvent. ...