Huh?!?! Why isn't this working?

Using NeroVision Express 3 to burn three AVI files to a DVD like I’ve done 1,000 times before. Now when I try to add two of the files I get a message that reads:

Unable to insert D:Movies/video - Title of file.avi.

Why? It can’t be the files because they play fine on my media player and one of the three is able to be added. Is there something I can do or check? SO weird.