This is a hardware issue. There are several possible causes:
1) Try another type of media. If you are using CD-RW disks, try a CD-R or vice versa.
2) Try another brand or color of media. Some recorders seem to work more reliably with certain types of recordable disks. Try finding a particular type that works well with your recorder.
3) If neither of the previous two have helped, it is likely that your recorder has developed a problem. Check with your recorder manufacturer for repair or replacement.
Resolving General Burning Issues