Approving an EMV transaction is actually a two-step process. Both the card issuer and the chip itself must approve the transaction. First, the payment request is sent to the card issuer. Once the card issuer decides whether or not to approve the transaction, it sends its decision back to the chip. The chip then has to make the final determination and finalize the transaction. The card needs to stay inserted throughout the entirety of this process.
This error means that the chip was not able to make the final approval.
This usually happens because the customer removed the card from the terminal too quickly. Ensure that your customers keep their card inserted until the terminal displays a message that they may remove it. In most cases the terminal will beep as well to indicate to the customer that it is safe to remove their card.