Have you linked a stockpile to your still?
If you have linked at least one stockpile to a workshop it will ONLY take from the linked stockpiles and not from others any longer.
If this isn't the case try giving the job order by the manager (jobs menue: j -> m).
I had this problem once with soap and once with steel. Couldn't queue the reaction in the shop but the manager could make it queue in the workshop.
Ah, that'll be it, I haven't tried out stockpile linking yet, I didn't know it was mandatory. Can you point me in right direction to get that done? Can't see any options in either my stockpile or my still.
EDIT- Never mind, found it.