Error adding Rates - Dates not unique for item

This error indicates a timekeeper has the same effected date twice.

To resolve this Error, Change your viewing option from "As of" (date) to "All", so you are able to see all history for the Rate Set.    Then select the Timekeeper column to sort.    You are looking for line Timekeepers that have the Same Date for the Same Timekeeper.  Once located, open one "Item" and advance the Date by one day.  Choose Save.