How can I avoid DVDDL back up error?

The DVDDL disc is not usable with Windows 7 backup. I am using DVD-R+ which is double sided to back up Windows 7. I have used once the same for back up and when I am trying to back up again on that disc it is saying it cannot back up to this disc. My DL drive is working properly, but the backup is not able to take again on the same disc. Is my disc full or is has a problem with my back up process? Please help me to get out of this problem. I will thankful for all the help and support.

Insert blanc disc
The disc you inserted is not blank.
Insert a disk and close the drive tray.
