From the article (translated with google translate):

Has happened before
Konsteien, Communications Director at Widerĝe, confirm the error in a text Aftenposten Sunday night.

"Hi. Amadeus has published error rates Saturday night without fuel surcharge. This was impossible for our system to detect, and it was apparently known through various online forums. Therefore, it sold many tickets relatively cheaply to the U.S.. Unsure if United will draw tickets back or maintain them. The last time this happened tickets were upheld and people could travel. Last night went fees for about 2,000 kroner to the U.S., "writes Kongsteien.