I don't have any experience with the free trials, but we do know that you cannot load an ongoing game that has been saved using certain EPs if those EPs are ever removed -- the game will either not load or it will be unstable with undefined things and errors everywhere. Sims created using EP content also require that content to stay in play in order to be usable. Not CAS parts so much, I mean things like traits, skills, and occult states. I assume your game is not in Bridgeport because without LN it shouldn't even be able to load as the world file won't be usable anymore.
How is it that this vampire can still exist if you no longer have Late Night? Do you have Supernatural? It's possible that SN-only vampires are not exactly the same creatures as LN vampires, and the game is not reacting well to the EP removal on that sim.
Can you start a new game now someplace else or do bad things continue to happen without the EP trial in play?
You may need to dump (pull out or rename) your TS3 user game folder in Documents and start with a fresh one if you are unable to play at all with or add store content to the current one in place.