Whenever I launch a specific book on my iPhone or iPad, it says that I'm not at the latest position and asks if I want to go to that position. The problem is that reported position is invalid (e.g. 999999). If I choose to go to that location nothing happens. Since I can not go to a further location, the last reported location is never updated and I cannot use this feature on this book. I'm looking for a way to reset this furthest location without it erasing my notes and bookmarks. Since this happens on all the clients, I am assuming it's not a problem with the individual clients and instead is a problem with the web service. I tried using the directions on http://www.mobileread.com/forums/showthread.php?t=84601 but since I don't own a Kindle, it doesn't work. 
How do you reset the furthest location of a Kindle book?
kindle
I had to contact Amazon's Kindle support and they reset the book's furthest location for me. This is the only way to do it at the moment.This was just confirmed to my by an Amazon representative. However, they did mention that they added it as a feature request, so this might change in the future.