You need to remove the install limewire.pkg file from receipts folder; Receipts folder sample image

erm .. might be worth deleting your LW preferences: Deleting LW Preferences folder in OSX

I also occasionally had same problem when trying to update to LW 4.18 or 5 on my main OSX system, in that LW 4.16 would not work any more after downgrading. But it did after deleting a few items.

If that does not work, lower the Java 6 level priority below Java 5 in Java preferences: Setting up Java for Leopard.

(hmm I wonder if your LW 5 issue was related to the order of your Java preferences. Difficult to say.)