Even before the advent of broadband video and video iPods, the $2 billion+ market for network television advertising was a house of cards, held losely together by the “Nielsen ratings,” a data set so deeply problematic that it may soon bring down the entire house.

MediaPost reports on a new tale of error and inaccuracy involving Nielsen’s new timeshift viewing data, which aims to account for the increasingly widespread use of TiVo and other digital video recorder systems:

IN THE LATEST IN A series of debacles stemming from Nielsen’s effort to begin including ratings for time-shifted viewing this year, the TV researcher has informed clients that all of the data it has released on an increasingly important metric – length of tune, or “LOT” – is wrong. The data, which calculates the average amount of time viewers are tuned to a network, program or daypart, is used by some advertisers, agencies and networks as a surrogate measure of “engagement,” an increasingly important but often elusive effort to understand how deeply consumers are involved with the media and advertising content they are exposed to. But in a series of notices sent to clients last week, Nielsen said all of the length of tune data it has issued since Dec. 9, 2005 is “incorrect.” That’s a problem for a number of cable networks, which have already made upfront sales pitches based on that data, and for advertisers, agencies and other networks who’ve incorporated the data into their 2006-07 upfront strategies.

“We understand that length of tune data is important for upfront presentations,” Nielsen acknowledged in its first client communiqué disclosing the SNAFU last Wednesday, adding that the glitch was “being treated as a top priority.”

Such “SNAFUs” are nothing new — but on the heels of Disney’s decision to make some of ABC’s shows available online, you can start to see the house of cards teetering.

Forget for a minute all the 2.0 talk about “liberating” TV content — let’s assume for the near-term a simpler 1.1 scenario, where networks merely move shows, complete with ads, online. Suddenly Nielsen’s data-sampling stranglehold on the market begins to loosen — advertisers now have data to measure EVERY time their ads are viewed online — and the networks, not Nielsen, are the keepers of that data.

Everyone looks around at TV advertising’s sham upfront “market” and realizes that the emperor is starkers. Advertisers and agencies have egg on their faces — you can almost hear the sucking sound as all of the ad dollars rush into broadband video.

What will the new online market for video advertising look like? What role will YouTube, Google, and other 2.0 players have? What ad models will emerge in a networked, digital, 2.0 marketplace for video?

I can’t say with any certainty, but I do know that life after Nielsen will be a brave new world for video advertising.