The American Stock Exchange (Amex) was hit by a technical problem, which prevented trading last Thursday.
The glitch, the second in a fortnight, forced the exchange to shut down for nearly an hour.
The latest problem is believed to be the result of mismatched ticker symbols on an exchange server. This affected trading in equities and exchange traded funds, but not options trading, but the exchange has yet to issue a full explanation.
The previous problem at Amex resulted from errors in a platform it is phasing out, which led to a halt in trading of stocks and exchange traded funds. "An issue occurred between our legacy CMS order entry gateway and our new system AEMI [Auction and Electronic Market Integration Platform]," Amex wrote in a statement on its website.
AEMI went live at the end of last year, in readiness for new US Securities and Exchange Commission’s rules that were introduced in February.
Stock exchanges are increasingly reliant on high-speed electronic trading, which means their IT servers handle larger and larger amounts of traffic. The London Stock Exchange recently introduced a new platform to help with this and its electronic order book, SETS, saw strong growth in its last financial year. Its recently announced £1.1bn takeover of the Borsa Italia group was centred on electronic trading.
In March, the Singapore Stock Exchange suffered a setback as its electronic trading system collapsed for more than an hour. Last October, the Tokyo Stock Exchange was sued by broker Mizuho Securities after a botched trade that resulted from a combination of human error and system problems.