The New York Stock Exchange said its nearly four-hour trading halt on Wednesday resulted from a technical problem that stemmed from new software rolled out the previous evening.

The unit of Intercontinental Exchange Inc said on Thursday that the glitch caused communication problems between one of its trading units and NYSE customers as they began connecting to the exchange at 7 a.m. EDT on Wednesday morning.

NYSE said it attempted to fix the problem before the market opened, but customers were still reporting “unusual system behavior” midmorning, and it decided to halt trading.

The exchange said it then began canceling all open orders and reaching out to its customers as it worked to solve the problem.

Trading in NYSE-listed stocks continued uninterrupted on other exchanges. The NYSE came back online shortly after 3 p.m., once the technical issues had been resolved.

(Reporting by John McCrank, Editing by Franklin Paul and Lisa Von Ahn)