Hello again...
I just thought I'd let you know that I managed to solve the problems with getting all the mp3's to play. Well, I say "solved"... I don't know WHY this worked but it did... maybe someone else can explain.
I was routinely renaming my mp3's using MediaMonkey, so that all the files had the track number at the start so that I could play albums under the folder tree and the tracks would play in the correct order... I wasn't moving or renaming any folders.
Lo and behold, MediaMonkey having kinda "recreated" the filename and/or folders meant that the files which used to just be skipped play perfectly! So, if anything I have INCREASED the ID tag length rather than trim them... I don't understand it, I just know it worked!
I should also mention that I discovered once I'd upgraded the firmware to 1.60, that most of my mp3's tags would not be displayed when played. I also fixed this with MediaMonkey by using it's "Advanced Tag Management -> Clean ID3v1 and v2 Tags..." function and then recreating them by performing the "Synchronize Tags..." function.
I'm wondering how these errors got embedded in my folder tree, considering as I said, that I have not changed the tree structure in anyway, the only change I made was to lengthen the filenames by 3 characters each!
Anyway, I hope this helps anyone out there who also had this extremely frustrating problem.
Mark