Ask in the Addons forum topic. It could be a Windows rights issue.

I have them all again now! I moved the M3U files that were missing to a new folder and re-scannd. Somehow ended up with TWO of every playlist instead of NONE, so had a lot of deletions to make.

Not sure if it's related, but my auto backup on close down is now failing, with this message:
"Backup cancelled because output folder could not be created."

I have created a folder called MMBackup, which I understand is what's needed, but no joy.

Thanks for your patience. Still missing many playlists. I'm including their folder in Folder monitoring but they do not get imported.

[img]https://www.dropbox.com/s/zbs5qdqgsfbfdrk/LostPlaylists-3.jpg?raw=1[/img]

That's likely where the problem is. You can't move files outside of MediaMonkey without breaking things in MediaMonkey (Dead Links, empty Playlists).

Either use MediaMonkey to move/rename files (best) or have Folder Monitoring enabled on the folder the files come from and where they go to or their shared parent folder and then move/rename files in Explorer.

I reckon my folders are in a mess. I'll focus on reorganising them and see if that restores order.

No, you don't need to keep the Playlist files, nor need to keep scanning them (but do keep them for now as you're having problems). Do you have Folder Monitoring enabled?

Complications!
1. They've somehow vanished again. IOW, many of the entries under Imported Playlists now do not disolay any tracks.
2. Must I keep M3U selected in the filetypes for scanning? But that creates a duplicate, one empty, one OK.
3. When I drag an OK entry from Imported Playlists to the main Playlists folder, it become empty again.

Clearly this is down to some mistake(s) I'm making...

Bingo - thanks Lowlander!

I'd actually already added them to my scan specification, but had forgotten all about that category 'Imported playlists'. There they indeed are.

Then just scan the edited Playlists into MediaMonkey. They'll be imported under Playlists > Imported Playlists.

As I said, I've done the global editing of the M3U files. It's all the rest that I find daunting.

It isn't. Advanced text editors like Notepad++ can do a Replace on all open documents (Playlist files). If for example you only changed drive you'd replace C:\ with M:\ (assume a change from C to M drive). If you changed part of the path too included it as well (ie. C:\Documents\Music\ to C:\Music\). Then import in MediaMonkey.

Thanks Lowlander, but that sure looks complicated! Suspect I’m liable to end up losing my entire database. Maybe I’ll just create all or most of my playlists from scratch.

You likely removed the old (non working files) from the Library and rescanned the new working ones which is why the Playlists are empty. As AutoPlaylists are Criteria, not file based they continue to work. Next time update the Path of the old files: http://www.mediamonkey.com/wiki/index.php/Moving_MM_to_a_new_computer

Now you'll need to change the Path of the files on the Playlists to match the new PC. Any text editor can do this and you often can use the Replace function to do it for all files. Then Add/Rescan Files to Playlist files to have them scanned in. You'll need to remove the old Playlists from the Library as MediaMonkey can't update existing Playlists (it maintains no link to original Playlist files).

Meanwhile, pending advice, I changed the M3U files to show the new links (D:\Music instead of C:\Docs\My Music). I then found and installed the script [b]ImportM3U.vbs[/b]. But when I run it and specify the folder containing the M3U files, it fails with this obscure message:

[img]https://www.dropbox.com/s/bsues3itbv8bqlu/Scrip-ImportM3U-Error.jpg?raw=1[/img]

That line 275 is even more obscure to me:

Dim trax : Set trax = dat.QuerySongs(sql)

And including the spaces at the start of the line, 'column' 21 seems to be a space, which seems OK to my non-techie eye?

It really can't be this hard to get M3U files into MM?

OK, after further digging I think I may have found the answer to my initial question. The data appears to be in files like these:
C:\Users\terry\Dropbox\MM Backup\1950s Favourites.m3u

Its opening lines are:

#EXTM3U
#EXTINF:197,Ella Fitzgerald - Someone To Watch Over Me
C:\Docs\My Music\Ella Fitzgerald\Sentimental Journey 23\Ella Fitzgerald - Someone To Watch Over Me.mp3
#EXTINF:188,Ella Fitzgerald & Louis Armstrong - Can Anyone Explain
C:\Docs\My Music\Ella Fitzgerald & Louis Armstrong\Sentimental Journey 126\Ella Fitzgerald & Louis Armstrong - Can Anyone Explain.mp3
#EXTINF:165,Frankie Laine - Dream a Little Dream of Me
C:\Docs\My Music\Frankie Laine\Foreign Affair-Reunion in Rhythm Disc 2\Frankie Laine - Dream a Little Dream of Me.mp3

So my new question becomes: how should I proceed now? I assume I need to use my text editor to globally replace all strings '[b]C:\Docs\My Music[/b]\' with '[b]D:\Music[/b]', which is where I now store all my tracks (in the same structure as on my old PC). [u]But where do I then re-locate the new M3U files please[/u]?

In an attempt to answer that I made a new playlist called 'xyz', added a single track, closed MediaMonkey and searched for a file with 'xyz' in its name dated today. But there was none.