Error messages usually appear when something in Kart Kingdom glitches and requires you to refresh the game. Clicking on the "X" or "OK" buttons automatically refreshes the page for you. There is an "Ooops, something went wrong! "message which might be a glitch, an "Oops! Something odd happened! Please refresh to rejoin the fun!" message, and many more messages. Some only happen once, most likely because of a glitch. Others happen multiple times.