Is Nero or my Burner at fault? 2 Coasters

Out of the 10 pack of Fuji DVD-R 4x Discs I have 2 coasters.

My Burner is a Pioneer A07 with 1.03 as the firmware.

In both cases I was burning DVD Video with the option to “determine writing speed” checked before burning.

If I dont check this option, and leave it at 4x it seems to burn fine.

In the instances where it did not work it gets to about 2%, the burn light on the drive turns off, and it just sits there, and about ever 20 seconds you get the cursor that changes to a CD indicating it is is seeking. Any ideas is if this is my Drive or the demo version of Nero causing this? So far I have 8 other successful burns, but some were made with Alcohol 120%. And as mentioned, some with Nero, with only Write checked, not the determine max burning speed.