In case someone else out there is searching the web, as I did, trying to figure out why their front lens element is falling off their 18-200 VR lens from Nikon, I will share my experiences with this. I baby my lens, especially compared to my bro-in-law; I keep it dry, I don't throw it ever, things like that. But, I do use my light hood a lot when outside; and since my camera and lens will not fit in my bag with the light hood on, I frequently reverse it back on the lens to store it.
A few months ago, the lens stopped auto-focusing to infinity at 200mm. Eric was around when this happened, so we swapped lenses and learned that it was my lens, not my camera. I learned that I could still focus manually, so I sadly shrugged it off. Then, just about a month ago when hiking in the Santa Monica Mountains, I noticed that I could not even manually focus to infinity at 200mm, and this really frustrated me. I also noticed that the front element felt a little loose. When I got home I inspected and saw that it was very loose!
I got online and started searching. I found a few threads around that indicated that their front element was coming loose and preventing focusing as mentioned above. Some people did not have the extended warranty I got for free, so they were fixing it themselves. I was still under warranty, so back to Nikon it went.
This was the best thread I found on this issue:
If this happened to you, good luck!