Ask the obvious questions first.
Are they bulk discs?
Does it happen to all the Discs?
Does it happen to an alternate brand of Blank Disc?
Has this problem occurred before?
Does the Disc work in another machine?
What does the Drive manufacturer say about that type of disc?
Does the drive need a Firmware update?
Is the Drive Lens clean?
What has changed if it is a New Problem, or since the last successful time it worked.
Alot of Bulk Disc have a quality assurance problem. I have found the blank Silvers from CompUSA to be trash, and this is very similar to bulk sleeves of Disc, bought through eBay and other outlets. Whenever I buy Disc in bulk now, through eBay or another Site, I Google the Brand to see if there is any Quality issues. Now I just got a really good deal on some DVD+Rs' 2.4x from CompUSA, I figured getting them for 25% of thier normal cost vs, taking 22 minutes to burn was worth the trade off. But get this... first Disc off the Spindle was Bad. Nero wouldn't see it. All of the others on the spindle have been fine. I figure the First and Last Disc in a spindle are crap shoots, owing to what I call the 'Handling Factor.' Being handled by machinery in packaging.