We found that the Purchasability Type for one or more of your In-App Purchase products was inappropriately set, which is not in compliance with the App Store Review Guidelines.
Your In-App Purchase is currently an Auto-Renewable Subscription. However, it would be more appropriate to use the Non-Renewing Subscription In-App Purchase type. Auto-Renewable Subscriptions are intended for periodical apps, such as magazines and newspapers. Non-Renewing Subscriptions should be used for products that are not appropriate for Auto-Renewable Subscriptions.
Nothing in Apple's documentation hints that Auto-Renewable Subscriptions are more appropriate for one class of app than for another, so I was hoping that my reviewer was acting on some subjective, high-level guideline that I could argue on. However, it's beginning to look as if there is a specific, unwritten policy against non-periodical apps.