Songs disappearing when i press play

The weirdest thing just started to happen. When i press play or double click to play a track it begins to play, but it disappears from my music list! I can't skip forward or backward in the play list. It doesn't seem to be re-sorting the list and moving it somewhere else. It just seems to be gone! I tried restarting iTunes and the songs that went missing do not repopulate. And they are still in their folders on the drive where they live.

It's a secondary library that i made of live shows that arent' in iTunes and bc i had too many tracks for iTunes Music Match. So i hold option when i launch. The tracks are linked to, not copied to the itunes folder. I stayed signed out of the iTunes store when i use this library so it doenst show all my Music Match songs. It had been workikng before. even after the 10.6.3 update.

Anyone seen this?

thanks in advance