In a document posted on the SEC's website Thursday, the regulator said the deal did not comply with U.S. rules governing stock exchanges. The SEC said it couldn't resolve concerns about the proposed ownership structure, which would have given 29 percent of the company to a China-based shareholder. The Chicago Stock Exchange couldn't supply documents the regulator requested about relationships among the proposed buyers, according to the SEC. Castle YAC Enterprises — a related ownership group, according to the SEC — would have had an 11 percent stake in the Chicago Stock Exchange.