This is essentially the same treaty that France and Holland rejected two years ago. It's been rewritten in an attempt to befuddle the opposition: some critics state that it has been simply rearranged in order to make it incomprehensible to the public. Also, some of the national legislatures of the countries voting on it, did not allow a national referendum. This essentially takes the decision-making process out of the hands of the voting public, who don't know what's good for them. Thus, those citizens who are opposed to it are, for all intents and purposes, disenfranchised.
The "problem" with Ireland, however, is that it's constitution requires a national referendum on matters such as this.
Ireland doesn't deserve the sole blame for this. A large number of European countries have yet to vote on it, one way or the other.