No it's on one of the internal HDDs in my Mac Pro and seems only to affect random tunes.
The only way I can find to work around it so far is to delete the tracks from the Mac and re-downoad them from the Cloud.
Seems very odd and is very irritating.Would be quite useful if I could simply do what do with my iPhone - access the music from the cloud rather than locally.
Mind you I still have two tracks from a Led Zeppelin CD of mine that were in the library when I turned Match on and are still listed as 'waiting' and greyed out 7 months later...!
It is not necessary to download the tracks from the cloud. They are most likely still on the HDD, but iTunes has lost track of them for some reason. Hightlight the track, Get Info, and when prompted to find the track navigate to where it should be and select it. The exclamation point will go away.
If, for some reason the file is not on the HDD, then it is also possible to restore it from the backup. But there is more than one way to solve the issue.
Bizarrely, the files appeared to have actually vanished from the library folder all together.
Each artist appears to have a folder within the library and yet the ones that had excalamtion marks had no folder.
All very odd since I never deleted them and they were most certainly there within the last few days, as I listened to some of them.
That is odd and, obviously, shouldn't be happening. Perhaps the files have gotten "misplaced" by iTunes. Are you able to find any of them using Spotlight?
I have two recommendations.
1. Make sure you have a current and complete backup of all your personal data immediately.
2. Boot into the recovery partition, open Disk Utility and run "repair disk."
I'm not saying this is the problem but there might be a bad block on the HDD or perhaps a corruption in the file system. Whatever the problem is, having a current and complete backup of all your personal data is very important right now.