I have noticed that sometimes myself. I don't know why that happens. For me it might happen to perhaps one out of every 10 or 20 files.

If you've dragged them & iTunes won't accept them, then something's wrong. Don't drag them from LW's Library window. 1st select Saved Files folder in LW's Library window & press Explore button. Then try drag & drop onto iTunes. There are some audio types iTunes doesn't necessarily recognise. I think rm which are real media files are one type & I suspect Ogg Vorbis mp3's also won't be recognised. That's why I have back up mp3 players such as Audion which does recognise Ogg Vorbis. I think Toast also recognises them. Another app that recognises them but also rm is Audio Hijack. You may need to convert them to aiff & then mp3/aac or a straight conversion if you want iTunes to play them.