Okay, lots of people have been asking about this on Darren Shan fan sites. Here's what happened.
Dark Calling, Book 9 in the Demonata series by Darren Shan, was released early. It was shipped early, you see, so the shops got it, displayed it, and evidently sold a few copies. Almost immediately after the very early release, it was pulled back. The recall left the bookshops empty of stock, had some fans wondering where it went after their mates got it, and after a bit of thinking from Mr Shan, left the remaining copies as collector's editions.
At the end of the book, there are a stream of words in Italics. I won't say why, only that they're important to the story. It's a thought, a memory, rather than speech. The initial ending was an "in-character" trait, and then there arose a problem. The publishers, by mistake, pasted the line: onclusion, coming October 2010
On the next page is the advert for Hell's Heroes, the final book in the series with the line Don't miss the Earth-shattering conclusion, coming October 2010
There are, as you can see, two mistakes there. Firstly, the word is "conclusion," which is an obvious indication that half-way through a sentance, the word was cut in two, and placed in the main text of the book. This raised the suspicions of readers who had the book - a mysteriously poor ending by Darren Shan? Nonsense!
They also got worried by the 2010 remark. That was also wrong... Here's what happened!
The books were recalled. All of them, mainly. Only 30,000 Hardback copies in the UK survived the recall, with a slip from Harper Collins being slotted into the books with the real text and an apology (from what I've heard.) These books are rare, and as such, valuable. Then there comes the Irish ones! None were left on the shelves, but some were bought. I have one beside me, limited edition, typographical error, one of only a few copies bought, due to the fact that fans weren't aware of the release.
Hell's Heroes is in fact coming out in 2009, on October 1st. It's something fans are dying for; the cover is too tempting to resist buying that book! Hopefully, it won't come out early with a typo....
Sources of reference: Shansters United on Bebo and the May 09 issue of Shanville Monthly