Missing files on I Tunes

[kelfoan]

I downloaded some music (legally) from You Tube. They were downloaded onto my I tunes library and played ok for the 1st 2 days. Now every time i try and play them a message appears that the file cannot be found. It seems asthough all the tunes expire after 48 hours. How do I save the tunes without then expiring. I had this happen again and the only way I could play them was burning them onto a CD

[Wak]

Only guessing here but it sounds as if you are only downloading the address on U-Tube where the tunes can be found. Once the tunes are removed from U-Tube your device can't find them.
Try to find a way of downloading the actual music and save it to your hard drive.
Google for the "FreeCorder" Tool bar as that will save music to your computer as you listen to U-Tube.