RPP stands for "Ran Pikes Peak"
It means that the runner indicated that they had previously ran the Pikes Peak Ascent or Marathon but name that the runner registered with did not match what is in the historical database.
I fix all of these as part of the qualification check process and no action is required on the runner's part. Most of the time it is just a missing middle name or initial, other times it is something like "Bob" vs "Robert."
--john