I've installed mm4 and used a copy of my mm3 database to have mm4 upgrade it. I manually put in it in the new location. After the database is upgraded some files (specific files, not random files) show strange behavior. When I try to drag or send one of these to a playlist I get the following error message:
I've checked and the files still behave fine in my MM3 installation. I've retried upgrading the MM3 database and the result is the same. I did nothing else between upgrading and trying to drag to playlist.
Now, I've had problems in the past with my database but those seem to have been fixed. You can read about this here: viewtopic.php?f=2&t=44507#p276930
I'm not sure if these things are related. I will try to see if I can see a common characteristic for all the problematic files. (none at first sight)
For others to see if they have the same problem you can easily check this by trying to mass sent all of your files to a new playlist and then check if the new playlist has the correct number of files. If the number is not correct an autoplaylist can help to filter out what the problematic files are.
If I sent more than one file to a playlist and the first one is not a problematic file I don;t get the error messages.