You'll usually get this error if you play from a file that was saved during the beta and before the scene with the ring was added. The option is in the first scene with Nerissa in Episode 7.

Hi there, sorry but this isn't an error we've seen come up before now. You may have to try uninstalling the game and then downloading it again, just in case something went funny during your update, otherwise, if it keeps happening you can click on the "Details for nerds" and either post a screenshot here or send it to hello@wanderlust-games.com and we'll look further into the issue.