Not to sure, but I saw online that Aberlour House is in Aberlour and it stated the date that it was built is 1891, but this cover was sent from Aberlour House Craigellachie in 1864.
The Walkers Shortbread Head Office is at Aberlour House on Spey and I believe that is the building which the cover was sent from in 1864
Anyway apparently this postal cancelation is very scarce