On the ps store I have bought Assassin's creed 3 liberation for the vita. When i go to download it a message pops ups and says "Could not ceonnect to server or device within the time limit nw-5603-4." The other downloads work. I have already tried removing my memory stick, restarting the psvita, and restarting my wireless lan router.
Since you've purchased AC3 liberation, try going into your download list and downloading from there. I've noticed since the implementation of the new store it likes to cut out during downloading while connected to the store, so what i do is I'll purchase the game, get out of the store, if on my ps3 I'll download it through the transaction management section on the ps3 or if on the Vita through the download list. Hope that helps.