The New York Stock Exchange was forced to suspend trading for several hours on Wednesday in the biggest outage to hit a U.S. financial market in nearly two years, unnerving investors already rattled by the meltdown in Chinese stocks and the Greek debt crisis. The exchange, a unit of Intercontinental Exchange Inc (ICE.N), reopened at 3:10 p.m. EDT after being halted shortly after 11:30 a.m. EDT. NYSE said the outage was due to an internal technical issue and not the result of a cyberattack.