Reformatting disk with no partition map
Remove all external disks (just for safety reasons). If possible also remove all internal disks except the boot disk or "refresh" your backups.

The proposed command (dd) used improperly can be deadly for your data.

Open Terminal.app and get the disk identifier of the disk containing the DVD partition:

diskutil list


Unmount the disk:

#replace diskX by the disk identifier of the "DVD disk" you found previously
diskutil umountDisk /dev/diskX


Overwrite the first sectors of the disk with

sudo dd if=/dev/zero of=/dev/diskX bs=4096 count=8


This will zero the first 8 physical blocks (or 8 4k/64 512b logical blocks) of the partition and should remove any "DVD hints".

Open Disk Utility and try to erase/repartition the disk again.