Nero 9660 format VS UltraISO 9660 format



I made an ISO image using Nero 6. My virutal drive could not read it.

I then made an ISO image using UltraISO. Virtual drive works with not problems.

Is there a difference in how the 9660 images are made between the two programs?

P.S. With Nero I created in 9660 and 9660+Joliet formats with no luck.