Some junk files will give you the 'already downloaded' error, even though you haven't downloaded the file before.

Try this: Use the All Types search > search for artist name or album name, rather than song title > choose a file with 10 sources or less, or even a file with a single modem source.

In LW click on your Connections tab. Now you'll see 3 or 5 hosts that you're connected to (number depends on whether you use basic or Pro). Right click on a host > remove. Do this for the hosts that you're connected to & new hosts will replace the ones that you've removed. Start a new search & see whether you get different sorts of results.

There are spam/junk files shared by companies who want to sabotage p2p. There are also lots of infected files being shared!! Make sure that you have a good antivirus program. Keep it updated & use it to scan every file that you download - before you open it

Look up files with Bitzi before download: How to use Bitzi
If other users have rated the file, you'll see whether it's good or not.

There are lots of fake files around now, which won't play. Have you tried playing the songs with different players?

Check out these threads for more info about what to avoid, some general virus info & info about fake files:
Virus thread: Typical virus spam file sizes - Make a note of them (click on blue link to see)

* WARNING: Viruses on network you should be aware of ! *

Fake files showing up in search results

How to find music