@nintendoom: corrupt video. did the Nintendo Video app update the SD card when the download finished? Did the download from server to 3DS even finish? all problems with a working setup IS corrupt video. redownload it and replace the ones you're hosting. once you start downloading the videos from Nintendo to your PC, take a note of the estimated file size (your browser should be able to tell you what's the full size of your download is, aside from what's currently downloaded). as for your 2nd and 4th panel videos, they're probably pretty old vids, which means you haven't updated in a while. they expired when you updated, is what happened.
@spinalcord: I've never really had videos expire on me. The only time a slot expired on me was AFTER i downloaded a few new ones and had no new video for that slot. so i guess videos does have an expiry date, but doesn't disappear until you update/replace at least one video. i'll hazard a guess that you can keep videoes for as long as you want, as long as you don't update.