You have probably seen it. You fill out a contact form, hit "submit," and instead of a 'Thank You' message, you get a vague, cryptic error page: ERR_CACHE_MISS. Or, you try to hit the "back" button after making an online purchase, and your browser flashes a "Confirm Form Resubmission" warning, showing the same error code. It is one of the most frustrating and confusing messages a user can encounter.
