Are you running any other apps in the background? Do you run other processes while cds are being burned?
Try this in Nero, File -> Preferences -> Ultra Buffer -> Manual Config and increase the data buffer size to about 50 MB. Additionally, as others suggested check with different media and try changing source location from current HDD to the other (hence you have two hdds).
Stone walls do not a prison make,
Nor iron bars a cage;
Minds innocent and quiet take
That for an hermitage;
If I have freedom in my love,
And in my soul am free,
Angels alone that soar above
Enjoy such liberty. - Richard Lovelace