Nasdaq was hit by a system error Wednesday that impacted thousands of stock orders, leading some to be canceled, according to people with knowledge of the matter. 

The exchange operator told market participants it’s investigating an order-entry issue that caused inaccuracies and delays, the people said, asking not to be identified discussing a private matter. Nasdaq’s electronic communication channel, which processes so-called financial information exchange or “FIX” messages, was affected, the people said. 

The incident, starting around 2:30 p.m. New York time, involving “certain FIX/RASH order entry ports,” Nasdaq said in an emailed statement that didn’t elaborate on the cause. 

“We are working to reach a prompt resolution to deliver the correct execution reports,” it said. The impacted entry ports will be closed for the rest of the day. The “closing cross was completed and all other markets are operating normally,” it added.

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Original: Fortune | FORTUNE: Nasdaq system glitch impacts thousands of stock trades and leads to some being canceled