Nero express burns nrg instead of DVD!

I have Nero

It had been working fine, but today it burned a
copy of the NRG file instead of the usable DVD that it should
have made.

I selected “disk image or saved project” as usual, then
luckily I checked it in showtime and found I did not have
a DVD.

I copied the NRG that it burned to the disk to another computer, using nero express ( using memorex) to make a copy of the NRG on my harddrive. Then used
express to make a DVD. It worked fine on that computer, with the old version of the software. ( It burned an actual playable DVD).

Any ideas of what happened?