The Ooops! Error message is an error message and a glitch in Kart Kingdom. It says, "Ooops! Something went wrong!" So far there has only been one report of this glitch happening. Most likely because Oops is spelled wrong.
The only report of it was in Grand Glade. A user was crafting karts and checking their field guide. But they tried clicking one of his karts in their field guide and this glitch keep happening. It happened a few times before they reloaded the page and tried it again in the same place. No glitch. It did happen once more a few days later, but it hasn't happened since.
They made a theory that this was a test or an unused error message the creators made, and it accidentally occurred to a few players or just one. It is unknown if this glitch will ever occur again. It is a very rare glitch now in days.