REPORT: A Barclays Trading Error Sent A Couple Big Stocks For A Ride

Closing orders were incorrectly entered, causing the transactions to be executed immediately, Mamudi writes, citing anonymous sources.

Among the stocks affected were Caterpillar, oil group Nabors, Nasdaq OMX and AOL. AOl saw the biggest swing, briefly declining 11%. Some of the transactions were canceled, Mamudi says.

Barclays clients weren't affected financially by the error.

Mamudi invokes the Knight Capital debacle, where a faulty algo caused $450 million in losses, to suggest exchanges remain vulnerable to these kinds of glitches:

Erroneous equity orders and their impact on markets have received heightened scrutiny since Knight Capital Group Inc. was pushed to the brink of bankruptcy when a computer program went haywire and bombarded exchanges with orders in August 2012. Last year, U.S. Securities and Exchange Commission Chairman Mary Jo White told U.S. market operators to review their rules for canceling transactions."

Barclays has not commented.