I tried to trace it, the error indicates that here: card/mod//05_standard/set/type/search_type.rb:174, the iteration var that should be a card (c) is an array that is displayed '[:error, #]' in the message. The search_results methods is returning that, which clearly is the wrong thing to do, but I can't tell anything about the underlying error triggering it.

yeah, I've seen this error, too. will try to hunt for it soon.