Conversion problems

Here's my problem in a nutshell...I use Limewire to download video files, then convert them,and burn them onto a DVD using Cucusoft. I've had some files downloaded,but when I go to move them to Cucusoft I'm told the file is empty!. I know it's not because the files play for me in my VLC player. Those same files have no time length note in the Limewire library. Help?....Anybody......Thanks