handbrake problem when converting dvd for ipod

[quidditys_shore]

i've just started ripping & converting my dvds to play on my ipod classic with handbrake.

first few were great but after that they just show up as an unknown file type (was mpe-4 movie with others). now i just wrote .mp4 at the end of each title which means they work but are a mp4 video file not movie. i'm still able to watch it but there are no chapters like the movie files have.

have i clicked something wrong by mistake? if not what extension do i give the files to make them mp4 movie? thanks in advance!