When adding files, it's necessary to add an extra file, because the first doesn't get included in the combined file. For instance, I need to add files like so: mp3wrap.exe -v 01.mp3,02.mp3,03.mp3,etc. The first file, 01.mp3 won't get included in the final combined file. I'm always combining at least 10 files or more. I'm using Win32 ver 0.5 on Windows XP SP3.
The first filename on the command line is the target filename. Put all the rest of the filenames after it, or a filespec if the names sort properly.