Well, the rules don't cover what happens if the only person to participate in a challenge is the person who set it.
Three options suggest themselves.
1) Leave the June challenge open for another month to give others another shot at it. 2) I post a new challenge for July and hope it's more popular than the June one. 3) Stop doing the challenges owing to lack of interest.
2 is my preferred option (and I have an idea for a challenge in which every featured book has been issued by Wizard (most of them twice over), so lack of availability of copies should be less of an issue), but what do others say?
I'm also out. I don't have time to even read the Sorcery! books right now (considering I've done the original series solutions, I think I've earned it). I should be able to get back into gamebooks in August. I have until then to hopefully get my life back together.