TPM did a little digging:

Well, it turns out that the ad, which attacked Romney on a host of fronts, seems to have run on Iowa television anyway -- at least a day and half after Huck promised at the presser he'd pull it, touting his decision as proof of what a noble campaign he's run.

This morning, a reader reported to us that the ad ran last night in Cedar Rapids, on TNT, during a rerun of Law and Order. And a day of run-arounds by the local cable company and unreturned calls by from the Huckabee campaign makes it pretty clear our reader is right.

That kind of deception doesn't sound too holy to me, HuckaBeLying.

So the mystery still remains. Did a bunch of techies forget to yank the ad because of extreme New Year's festivities. Or did Huckabee's media folks fail to put a rush on the yank order? No one's talking.

And how ironic is it that it played during an episode of Law and Order? 

The video is of his press conference where he showed the ad he said he was pulling.