SUMMARY: My experience indicates that FAT32 formatting allows correct syncing if the card is empty, but still failure if there is music already present from an earlier sync.
Set-up: Samsung Galaxy S3 with 64GB Sandisk Ultra SDXC card, MediaMonkey V184.108.40.2061, Windows 7.
11,500 files, all mp3, with configuration to convert high quality files to 128kbps
Card was exFAT format. Tried to sync music collection. Over 2000 failed to sync with a 'problem while copying file' error.
Looked at advice on this forum and reformatted the SD card from exFAT to FAT32
Synced music collection again, successfully with only one file failing to convert (a DRM issue).
I thought the problem was solved BUT
Tried re-syncing a couple of days later. In reality there were only 18 new files and no other changes, but MediaMonkey decided it needed to sync 904 files.
The 'Capacity' bar indicated there was 4GB of new data to sync, but in reality only 80MB of new data.
A large number of files failed (possibly all) with 'Problem while copying file C:\... to \Music\... ' errors.
* The one genuinely new directory did not copy over, but it copied over fine using Windows Explorer later.
* I checked a sample of the pre-existing failed files on the SD card and PC and the file dates were correct, ie it should have been clear there was no need to sync the files.
* Two of the pre-existing folders which I checked were deleted on the phone, ie MediaMonkey actually deleted the SD card directories. One of these folders had files which did need converting to a lower bit rate whilst the other did not.
* The other pre-existing folders I checked were still there, with dates unchanged, ie the files had simply failed to load.
The 'Capacity' bar was now showing 3.5GB left to sync so perhaps some of the files did copy successfully, though not the ones that actually needed copying unfortunately.
By the way I tried 'Save as Playlist' as invited from the errors window but it resulted in a playlist with no entries in.