MP3 files which cause this player to crash

I recently resumed adding files by drag & drop to an e280 with V15 software. It crashed after the third folder with some 23 MP3 files was added. I used the recovery software provided by SanDisc and that took the software back to version 12. First thing I did with this was to load (drag & drop) all 48 folders that I knew worked with version 12 onto the player together with a copy of the System Data folder saved from my first e280 (which completely died from a hardware failure). I had one track that had always failed before which I omitted (This one I copied to SanDisk who confirmed that it crashes the player but have no advice on why) So, I re-ripped it and added it in a new folder of its own. Everything worked fine using the V12 software. So then I connected to the internet to upgrade the software. This loaded OK and V18 was loaded but the player then crashed again during a data base refresh function and the screen went to its now, too familiar, bright but blank mode. I put the player into recovery mode and went back to V12 software. There I deleted all the folders and files from the Music folder on the player. When I removed the player from the PC and restarted it I found that, in spite of the PC showing that the Music folder was empty the re-ripped track and its folder still showed on the player and actually played! It still did after a link to the internet and an upgrade to V18. Now with version 18 running I dragged and dropped my folders of MP3 onto the player, checking that they played OK after each folder was added. By this means I managed to get 32 folders, about 700 tracks, onto the player (still with the phantom re-ripped folder). I had two folders which caused the player to lock up during database refresh along the way but by omitting them was able to move on. Each time a crash occurred I had to reinstall V12 and then upgrade to V18 and start again. Painful but at least I was progressing and I planned to re-rip all the files on the folders which failed as working through one folder at a time to find the problem ones would take too long. Finally I tried to add one more folder which I knew from my first player would work on V18. Except this time it didn't and the player went into its crash display when doing its database refresh. Alas this time the unit won't allow me to get it back to V12. When set to recovery mode and the e200fw01.00.12.exe program from SanDisk is run I get a "Application failed to read the version data" message and the program finishes. The player will then power up but still crashes once it gets about half way through its data base refresh. Any one got any ideas on why some files don?t work, why some files work on V12 software but not on V18., and how can I identify the dodgy ones as they all play fine on various PC based players and on 4 portable CD players, one micro hi-fi player and one car player using SD memory cards?