There's no activation code for Pro.

Where did you buy LW from, how long ago did you buy & did you buy 6 months or a year's worth?

You can only download Pro for free if you bought from the official site Lime Wire » Official Website & Free Download, BitTorrent « & if your benefits are still current (ie if you bought 6 months worth of Pro but you paid more than 6 months ago, your Pro's expired).

If your benefits are still current, either go back to the original email that you recieved when you bought Pro...it will have a link to your Pro download page.
Or go to the page below & enter the email address that you used to buy Pro.
Lime Wire » LimeWire PRO Lookup

If you did buy from the official site & are sure that your Pro hasn't expired but you still can't download it, send a PM to limenathan & see if he can help.
limenathan (click on link)