It may be related to this: Downlds refuse to reload (click on link)

For Mac OSX you should run the following program to backup your LW downld preferences: utility that backs up lw's downloads.dat/bak files automatically for mac os x here

Files in your library that are red (excluding your incompletes) are files that are no longer being shared. You can control-click them & choose to share again.

Incomplete files that have turned red have lost their relationship with their partner in the download window. You can resume them. But check to make sure you haven't already downlded other copies of the same file. Sometimes a downld may create more than one incomplete file.