Make a note of all your LW settings. Then close LW & delete your LW preferences folder found here: /Users/your_username/Library/Preferences/LimeWire

I don't know the reason for the problem. There are some characters that can't be used to save a file in OSX that's all I know. But I don't think that's the issue. Hopefully it's only a corrupt prefs setting(s) that's the issue.

As far as incompletes go, yes I tend to collect large numbers also & not willing to let them go because they're all rare files. But just in case, have you seen this: Recognising fake files

BTW if your incompletes are more than 18 months old, then there's a high possibility LW won't be able to continue them due to the differences between LW now & back then. In which case you might want to consider this Tip: Purge the Downloads Queue!
I did it recently but arranged my incomplete folder by date & got rid of the old ones. Actually some of the audio & video files were still playable so I've kept them for use but removed from incompletes folder.