as rapid fire has said, if you're making a SL backup, there is no layer break.
this is likely one or any combination of the below possibilities:
1.) poor media. please post the Media ID code of the blank media you're using. (Media id can be obtained from the disc info tab of nero cd-dvd speed)
2.) burning too fast/too slow. what is the rated speed of your blank media? burn at that speed or one "notch" below. never use the "max" setting.
3.) outdated firmware. check the manufacturer's website for your drive to determine if there are any firmware updates available for your drive. F/w updates often improve write strategies on a wider array of media so this may improve your burn qualitiy.