SuperDrive Error

Using Roxio Toast Lite to write DVDs I keep getting this error:
Sense Key = Medium error
Ense Code = 0x0C, 0x08
WRITE ERROR - RECOVERY FAILED
It happens at at different times, sometimes when it's almost done, sometimes when it's just started.
It still reads DVDs and CDs no problem.

Would cleaning the lens help, and how could I do that?

Any Ideas?

Thanks

decrease the size on DVD content. sometimes it helps