Hi all.
I think I've found a solution, I just bought an iPod Touch 2G, I have thousands of existing mp3s but was having the following problem:
1) A large number of my mp3s would not play on the iPod Touch
2) The ID3 tags seemed to be in order
3) The mp3s would play in iTunes no problem on my PC
4) After trying to play one of the affected mp3s the Ipod would often become unresponsive
You can do one of the following to fix this depending on your environment and your own preferences:
1) Converting the tracks to AAC (mentioned above) using iTunes works fine but I did not want to convert all my mp3s to this format (yet), and it was a slow process.
2) Converting the tracks to mp3 (yes from mp3!) using iTunes also worked but doing this with iTunes was not ideal as it renamed them and put them in the same directory
3) Download foobar2000
http://www.foobar2000.org/ Its a free mp3 manager and player for Windows, add the directory with your mp3s, select them all in Foobar, right click on them and select "Utils->Rebuild mp3 Stream" (make a backup if your worried). Synch these mp3s with your iPod using iTunes
Number 3 worked best for me as it was a bulk operation and converted the existing files rather than making a copy. It must be something to do with the old software I used to rip from CD to mp3. Foobar2000 (and obviously iTunes) will write the streams in such a way that the Ipod Touch is happy.
I also have iTunes configured to keep a copy of my music in the iTunes folder and to manually synch but I don't think that affects the solution.
James.