Yeah, we need more information. For example, Zune software does not work with .avi (divx/xvid) files.
Here is a list of the supported file types:
Format | File extension
AAC audio created with AAC-LC audio codec | .m4a and .m4b
Windows Media Audio | .wma
MP3 audio | .mp3
MP3 playlists | .m3u
MPEG-4 media created with either the MP4pt2 video codec or the H.264 video codec and the AAC-LC audio codec | .m4v and .mp4
QuickTime movie created with either the MP4pt2 video codec or the H.264 video codec and the AAC-LC audio codec | .mov
Windows Media Center DVR (Windows Vista Home Premium and Ultimate only) | .dvr-ms
Windows Media Video | .wmv
Zune playlists | .zpl