Multiple errors in log (paths and tags look ok)

[Barbie-qu]

NAS: Synology 213 running DSM 6.1.1-15101 Update 4
Music management: MusicBee 3.1.6345

Hi,
I was inspecting my MinimServer log after realising that a lot of tracks were not showing up in my playlists (mainly), and saw that i have a huge number of errors logged.

There are four type i see.
1] incorrect value for DATE tag
2] conflicting ALBUMARTIST values ignored for album 12 Inch Dance: 80s Pop
3] unknown folder for ../../Music_Tom/Various tracks/#. 100 Hz - Catching Spiders.mp3
4] no matching file for ../../Music_Tom/Compilations/Bleep + Warp/Bleep 100 Tracks 2011/10 - Borngräber & Strüver - Dancing Queen.flac

For [1] I am assuming MinimServer only reads dates in a YYYY format. I can fix this in my tags easily enough
For [2] I understand that if two tracks are tagged with the same album, but different album artist then I get this error. This can also be easily fixed.

For [3] and [4] i'm stumped. The 'unknown folder' and 'no matching file' errors form the majority of the errors, and they all occur in *.m3u playlists.
Most other files are indexed without problem in the playlists, and i can't see any obvious differences in the way they are tagged - I'm pretty careful about this.

As background, i create my playlists in MusicBee and save to a folder on my NAS. This folder is then indexed by MinimServer along with two folders that contain my music files.

Any help would be appreciated

Edit: i can see that a lot (but not all) of entries have extended characters which have not been recognised. I know this has been written about elsewhere on the forum, but do you know if there is any issue with MusicBee?