Albums eventually stop working/playing, stay in iTunes, will play in other

Question

I have abotu 5400 songs in my library, about 90% are MP3s I have ripped from my CDs.
Recently I have noticed that certain entire albums which have worked in the past stop playing... they are still listed in the library, the files actually reside where they are supposed to, and the MP3 files will even play in other apps like Windows Media Player.
Sometimes files like this will still play on my iPod. In most cases, though, if I were to navigate to that particular album on my iPod and try to play it, the ipod would attempt to play each track for about one second, and pretty quickly skip through the entire album.
When I click on them in iTunes, nothing happens. No error, just no response at all. I also notice that when this happens, the "Album Artwork Not Modifiable" message comes up in the album artwork window. I checked to see if these files had somehow become read-only, but that does not appear to be the case. All of the play history for the tracks is intact.
Most of the library is fine.
Any ideas?

Answer 1

Otto,
"I have absolutely no idea what would break an M4A file, though. Different tag methodology entirely"
Here's what I posted in the lounge....
- Song is in an Apple Lossless format
- Song file is present and visible within the Windows Explorer
- Properties indicate that it is not Read-Only or Hidden
- Properties can be changed back and forth within WinExp
- Song reference visible but not playable within iTunes
- Reference cannot accept any Album Artwork (Not Modifiable message)
- Other attributes can be modified: title, album, artist, etc.
- Song cannot be converted within iTunes (comes up as a 'null' song: no time and minimal filesize)
- A copy of the song made in Windows environment and moved to a temp folder cannot be successfully 'Added' to iTunes. Result: no time and minimal filesize
The song came in originally with a boatload of text in the title, artist and album. I am wondering if the ID tags are somehow corrupted, and preventing the song from playing within iTunes. All other songs from this album are playing fine.
When attempting to play this particular song, the speaker flashes for a second, then moves to the next song in the list. The time slider-bar does not move off of zero.
I have tried to change the start time, but that does not change its behaviour.
And...
It's an Apple Lossless file of 3:15 in time, 22.6MB in size, and listed at 969kbps. The size corresponds favorably to other files of similar length. The time listed is spot-on to what Allmusic.com has listed for it (Ringo Starr and His All-Starr Band - You're Sixteen, You're beautiful and You're Mine - Anthology...So Far).
Other than that, I cannot tell if it got corrupted.
I did download and install Tag&Rename to look at the file. It gave me a jpg error when viewing the file. I erased the 'garbage' in that tag, but after saving, the file would still not play within iTunes. Tried to erase all tags with a backup copy, but that did not play as well.
I don't have access to the original CD, but will in a few days. I can try re-importing it, but it would be nice to understand what went haywire -- or at least have a method to investigate it further.