Multiroom receiver + NAS + playlist

[frankcasier]

Hi,

I'm writing this in English because my German is not good enough.
I have 3 multiroom receivers in my house connected to my LAN network. On my LAN network I have also a WD NAS (MyBookLive) with all my music (in Flac) files in folders.
I have also made a couple of playlists. These playlists just reference to the network place where you can find the music files.
I have a playlist with x-mas music, one with James Bond music, a disco playlist,....

I've made these playlists with VLC media player, I've saved the playlist in the *.m3u file type.
Here comes my problem : recently when I changed the playlist (ad a song for instance) and save it again, the multiroom receiver (via the assist media remote control) says it can not read the file, wrong file type ??
How is that possible ?
The other playlists have no problem, I can still play them.
Can anyone help me with this ?

Thanks
Frank