I've had this problem, and several others, for every version of nero 6 through to the Jan 17, 2005 version. Tech support has been little help (i.e. - they reply, after a week or so, but don't fix my problems). I paid for the ultra-edition retail box; plus got it free with a memorex burner. I think I deserve it to work as advertised.
I've done a format of the hard drive, fresh install of WinXPHome SP2, and Nero, with no other software, hoping to eliminate any driver or software conflicts. Quite time consuming, that was. And still it doesn't work. Would love to know why.
My other probs, in case you have them too...
2) The option to encode in Nero Digital in 5.1 Surround Sound is grayed out. I can encode in stereo. I can burn DVD's with 5.1. But not mp4. I only have one audio codec where on an unlicensed version I once had there were two.
3) Nero BackItUp option to burn remains grayed out. Nero Burning Rom works to burn the same data.
Hope someone can tell us if it works for them.