In general, we have limits on check-ins in the past few minutes and last day, so if you've exceeded those limits, you'll see the rapid check-in message and not earn points, badges, or mayorships when you're over the limit (it's a rolling time period). If you've either been checking in faster than the system thinks you can travel, checking in a lot within those time periods, or consistently checking in to venues when the system thinks you are far away, you'll run into location troubles. (This also happens if you check into places that have vague location, like a town or neighborhood--that will skew your location and make it more likely for you to get location error messages). Make sure to only check in where you are at the time, and not go crazy with your check-ins and things should work ok!