I have a problem erasing my Sony DVD+RW. I've had no problems for a couple of months, then when I want to erase data using NERO I got message that disk can not be erased or has unknown format. I've been using disk disk for a while and erased it probably 20-30 time without problems. Is this disk bad or my DVD drive has some problems with this DVD+RW. I have to mention that I can erase CD-RW disks.