Same problem as sweaterjunkie
I am having the same problem as sweaterjunkie, except the ebook I downloaded was already in the Mobi Pocket Reader format (although it has a .prc extension instead of the .mobi extension mentioned above), so no conversion was necessary. At one point I got it to work just fine on my Droid phone with my Kindle app, but then I decided to push my luck and manually copy some other books into the kindle folder on my droid, causing the force close problem to come back. I removed the offending books from my Droid entirely, but it still force closes every time I try to open it. I have even tried removing the book that was working previously and then copying it back to the kindle folder. As long as it is not in the folder, the Kindle app opens just fine and I can see the books I have downloaded from Amazon through the Kindle app. As soon as I copy this book back into the kindle folder, it force closes.
I have also tried creating a sub-folder on the Droid's SD card under the kindle folder and placing the book in there instead, but Kindle does not see it.
The book opens and reads just fine on my PC with the "Kindle for PC" app (in fact it works better than it did using the Mobi Pocket Reader app, which it supposedly was designed for). My PC recognizes it as having a format of "Kindle content". Any thoughts?