Cd/DVD drive problems

I have both a cd drive and a dvd drive. I'm running XP Sp2 with all updates
installed.

I have a peculiar problem: When I run Nero I have no problem reading or
writing To either drive. I can play music or movies with no problem.

I run a backup program and I'm copying data to a round robin of DVD's. This
mean that I remove the backups on the oldest disk and backup the current
data to the same disk. All of a sudden When I try to reformat the DVD rw I
get a message that this is a DVD r disk and cannot be cleaned out. I am
unable to copy my data onto this disk.

I tried several disks so it's not a single disk problem.

I tried a DVD-r disk and that worked ok. I am not able to reformat that
DVD -rw disk. Is there some freeware that will let me clear out the
"writing" on the disk.

Your help is appreciated.

Regards,