Official comment
@Barry > Chances are you're allowing iTunes to manage the file locations (check the iTunes preferences and look at the Advanced tab):
If you change ANY of the metadata listed there, iTunes will automatically rename or move the file for you.
You have two choices...
1) relocate the songs manually - this could be time consuming depending on how they've all been moved since you won't likely be able to do a global relocation (a global relocation is if you moved all that music by one scope; for example, it used to be in a folder named "Music" and now it's in a folder named "Old Music" -- all of the music moved by the same amount, so the system can relocate it all easily)
2) remove the missing files and re-sync them -- after disabling that preference in iTunes.
