There is probably something wrong with the ebook. Try reading it in some other way such as the Calibre viewer or ADE. Or delete it from the KT and then add it again.
Another reason for this to happen is if the database in the KT is out of synch with the ebook. What happens is that when a ebook is first put on the KT, it will process the ebook and create database entries for each chapter. As you read the ebook, the database will be updated to record the current place. If you replace the ebook with a new version, the database isn't updated. From what I have seen, if the new ebook has new chapters added at the end, it is OK except they won't be in the contents list. But, if a chapter is removed in the middle, it can cause the problem you are seeing. Deleting and re-adding the ebook should fix this.
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