It failed because when you don't have anything funny in the trailer, then you are doomed.

Okay, the gag at the end where he grabs her humps was funny. But damn, a 90 minute comedy should have at least four or five jokes to put in the trailer. Right?

@Jim,
EXACTLY. Besides, spoofing vampire movies is hard. They didn't seem to use the fact that comedy is never funny to the participants.
Everyone seemed to be "acting."

It's clear the filmmakers couldn't decide what it was supposed to be.

If it's to be a spoof, it needed more outrageous gags like in Scary Movie. Instead, it was kinda a PG-13 Porky's with a whiff of Transylvania 6-500.

I was waiting for more gore, or sex or fart jokes -- something.

And who's story is it? The girl narrator, the Vampire hunter, the guy who looks like the vampire, or the vampire woman?

The problem?

MARKETING

There's clearly some funny moments and good characters.

But what is the story??

The trailer doesn't convey the POINT of the film... Why are they in Romania? What has happened on their trip? Who is after them? What do they want? What is at stake???

Hardly any of those questions are answered. As moviegoers, we need to know what we are paying to see. But in watching that trailer, we just don't...

So we're choosing to watch movies that make us a promise, hoping that the movie follows through and delivers on that promise... Transylmania makes no promises. It shows us some funny moments, funny dialogue, and that's it. It makes no promises that it will be a journey of teens fighting vampires, or vampires kidnapping teens, or kids discovering a new culture, or blah blah blah. It just makes no promises.

Promise me something! And then I'll pay to see if you deliver. But promise me nothing and I have no reason to give you my money...

Looks like the marketing team just learned a mammoth of a lesson... Either that or they're now working at Starbucks :(