TD Ameritrade Holding Corp , parent of the biggest discount brokerage by trade executions, is experiencing “widespread” problems executing orders, including those it has accepted, company officials said on Friday morning. The company is not yet aware of the cause of the problem, said Chris Gulick, who works in the Omaha, Nebraska-based company’s office of the president. “We are having some order issues and are working to resolve,” trading product head Nicole Sherrod wrote on Twitter.