Missing a file?

I installed Lightroom 3 upgrade last night, was using LR 2 up until then. Lightroom 2 was not unistalled, in fact it is still functional - not what I was expecting. Today I went to look at a file and discovered that the file is listed but all the photos in that file are missing. I would really appreciate any help you might have in identifying what's going on. I see that the file is present in my Time Machine backup (separate external harddrive), using an iMac. I really don't know how to move the file up to present from the backup.

Gary, I had a similar event last week using LR2 on my Mac. It may not be relevant but after looking all over I eventually found the missing files in the trash. I don't know what I did to move them there but easily recovered them once found.

Thanks Craig. I'm always emptying out my trash without checking what's actually in there. I'm happy that I managed to restore the file from Time Machine. Whew!!! A bit concerning thought that I have no idea where that particular file went.