Just now, Arena, any area. Last action: placed a crafted necklace at the market for sale. Re-started the game, no change. Went to dailies, same problem. Removed the necklace, no change. Went to a regular dungeon, same problem.
Before placing necklace at market I was equipping/un-equipping stuff and selling it at the shop.
So finally I cleared the cache. No problems after that at the Arena, but the problem persists at the daily missions.
Also, I've noticed something else: I accepted a Daily Mission but did not go to the dungeon immediately because I needed AP (got some from friends). I then tried to go to the dungeon through the Quests interface. But although the Quests icon (City, top left) was highlighted, the dungeon in question wasn't listed as it should have been.
So there's definitely a problem w/ the dailies but also w/ the arena. And I'm not sure it has anything to do w/ placing a crafted item at the market. Very weird...