There is one bottle that's sitting on the sea floor at the Mermaid's Grotto dive spot that your sim won't be able to get to. The sims can't get to it because it's sitting up against a tall kelp. The only way to get to that bottle is by unlocking that lot in edit mode, and then move it away from the kelp. The bottle is up against a tall kelp directly across the lot from the cave that looks like a fish's head. To unlock the dive lots for editing. Just simply type in testingcheatsenabled true. Then type in enablelotlocking true. Then you have to click on the padlock to unlock the lots. To move the stuck message in a bottle, just simply open the cheat bar again and type in moveobjects on. Now you are free to move that bottle any where on that lot any place you like. :D