Can't add audio to DVD project in Nero

Hi. New to this forum and hope someone can help. I’m making a DVD slide show in Nero Vision Express 2 and am trying to add audio files from my personal disc collection and from downloaded songs purchased online. When I use the browse for media button, pick a track out of my downloaded songs folder, and click open, the program tries to add the media and then I get an error message stating Unable to insert C:(file). I also can’t get tracks off of discs, even after I put them in a folder on my hard drive first (as the software makes you do). What gives??