Dvd recorder completely scratched two discs--why? ?

I have a Panasonic DMR-EZ 485V that recently did the following to me.

1. Put disc in--horrible sound from unit and when I removed disc the whole disc was scratched up.

2. Put another disc in--same thing.

3. U99 error code on unit.

4. Tried again and now unit functions OK---for now.

What would cause unit to deface two good discs that were viewed previously with no issues.