The funny thing is that I don't actually know because I couldn't see it. I was able to detect the problem by validating your feed by entering it at http://validator.w3.org/. This showed me where the problem lay. It reported an invalid character and showed me where to look in the code for it. I then edited the affected post, moved my cursor to the spot in question, and arrowed back and forth. It's easy to miss, but in these cases, the cursor won't move when it hits an invalid, hidden character. That is, it'll move over until it hits the phantom character, not move the next time you press the arrow, then move again the next time you hit the arrow. It's basically arrowing past a character you can't see and thus appearing not to move at all. I think these things usually land in code via copy and paste. In this case, it was adjacent to a period in the text highlighted for an Amazon link.