By the way, the format of the delta did change (from an older 0:0:0:4:0:0:0 to a newer 0:0:0:0:96:0:0) to handle the fact that a day was not a constant length period of time. That change was quite a while ago though, so I wonder if you upgraded Date::Manip recently after a long period of using an older version. That would explain why this just started failing for you.