Converting .AVI to .MP4 for iPod

[llllozzajh]

Hey, i use videora for converting my videos to .mp4 so i can watch them on my iPod, but, recently, some videos convert then state that they cannot be added to iTunes library and the newly converted file cannot play. I dont know if it is linked but the videos in question do not display what their default program is (Realplayer, Windows Media Player, Winamp). Thanks In Advance.