How long ago did you buy Pro & did you buy it from the official site Lime Wire » Download LimeWire ?

If you bought from the official site, then your Pro benefits must current for you to be able to download Pro for free. What that means is: if you bought Pro (6 months worth of free updates & support), it needs to be less than 6 months since you purchased.
The Extended Pro (12 months worth of free updates & support) was introduced in August 2007.

Providing your benefits are still current & you bought from the official site, go here & enter the email address that you used to buy Pro: Lime Wire » LimeWire PRO Lookup

Or, if you've saved your emails, go back through & find the email that you recieved after you bought Pro. It will contain a link to your personal download page, where you can download Pro