Try these 2 things:

1. Close LimeWire. Delete the LW preferences folder found here: /Users/your_username/Library/Preferences/LimeWire
(Note: next time you open LW you will need to reset all your options so make a note of any important settings. )

2. Tip: Purge the Downloads Queue! & apply it to files that are zero % downlded & less than 50 KB.