Wimbledon organizers have apologized and explained that “human error” was the reason behind the electronic line-calling system being turned off during a match on Sunday.

Sonay Kartal was knocked out of Wimbledon after her Russian rival claimed the British player got special treatment when the electronic line calling failed on Centre Court. Anastasia Pavlyuchenkova, 34, recovered to knock the last British female out of the singles 7-6 6-4.

Anastasia Pavlyuchenkova suggested her British opponent may have received preferential treatment as simmering tensions around Wimbledon ’s use of electronic line calling (ELC) instead of line judges boiled over Sunday,