Happy to thrown in my experience. As I was getting that same error.
Turns out Rachio needs 24 Hour Rain Value data. The reason I wasn't sending it was due to the fact my VP2 and WeatherLinkIP needed firmware updates. Once I did those it began to work properly. You can find them here
hope that helps... I will also tell you once you complete that it does take a few full days for the Rachio system to account for the new data. Franz, who has been amazingly helpful through all of it, was kind enough to confirm they were getting the data before the error stopped appearing.