henkybaby following on from stargolds post if you look at https://www.oneworld.com/ffp/lounge-access for ARN you will see that you only have access to "Stockholm Arlanda Lounge" because all lounges at ARN are third party lounges. You should also consider the conflicting opening times given for the lounge!
The Oneworld lounge page is usually very up to date and accurate. But it has slipped a little in recent months.