Virtual DJ has two options for playlist export.
The first is that any playlist created or imported by the user will automatically appear in their Documents > Virtual DJ > Playlists folder. This folder is created during the initial install and setup of VDJ.
This is the playlist file you need to select when importing to MIXO as it will contain all of the filepath data needed for each track.
The second is by right-clicking the playlist within Virtual DJ and selecting Export Playlist from the context menu. When exported, this will copy all tracks within the playlist to the specified location. This is fine for using the playlist within a media player, however as the file does NOT contain any filepath data, MIXO will be unable to import tracks from this file.
Please make sure to use the first method when importing Virtual DJ playlists.