Just because the disk says its 8x does not mean that it will write at 8x. It could be the DVD writer doesn't like the brand of disks or perhaps the burning program doesn't. All disks are not the same. My mates DVD writer likes the cheaper disks and doesn't seem to like some of the more expensive brands. The only suggestions I have for you is try various brands or have a look on the DVD writer manufacturers website and see if they recommend a particular make of disk.