1) "Sliding bookcase door" - works perfect till you move the a lot from its original building spot and place it somewhere else. Your sim will not go through it . Solving this problem is easy - just grab the bookcase door and place it again.
2) "Alchemy station doesn't let you mix elixirs anymore" - Well check out your bags. If you have any SEEDS in your bags remove them (drop them on the floor somewhere) and mixing should be possible again.