this error got me too;
after some poking around this works for me as a workaround :
1. Go to tp npc till you see the talk button (don´t press f right now)
2. right click any item -> sell on tp -> click cancel -> press "f" to talk to tp npc -> now you can sell and buy normally
!! trying to get into Gem Store from there crashes the Game!!
maybe this is caused by anet changing the payment provider?
it does for me : [&DQgTPjUbMisoD6IAdwEAAHABAAB1AQAAkgAAAAAAAAAAAAAAAAAAAAAAAAA=]simple copy template, paste here.(new necro: pls do not comment, just created him)
Maybe this´ll help with trying out Controller via Steamhttps://www.reddit.com/r/Guildwars2/comments/9w1pbk/complete_xbox_controller_support_for_gw_super_fun/
"Double click to summon your skyscale. This will complete the nearest Skyscale Lost collection item on the map. If no such collection can be found, this item will not be consumed " https://wiki.guildwars2.com/wiki/Extra-Pungent_Skyscale_Treat