Reputation cannot be recalculated more than once per day.
I am positive it was more than a day ago. Hard to argue with a machine though. Anyway, it is a good workaround for an obviously wrong rep total for a day.
It is painful to use though, the feature is blocked by a 24 hour interval, it doesn't go by day as the message says. In other words, it doesn't reset at 0:00 UTC, you have to wait for 24 hours or more before it can be used again.
Which requires an alarm clock. Please allow recalcs in, say, a 23 hour interval.