How long ago did you buy Pro?
Did you buy Pro from the official site?
http://www.limewire.com/
Did you pay LimeWireLLC for Pro (check your CC statement)?
Did you buy Pro for a year or 6 months?
Your email address will only be recognised in the official database while your Pro's current - if you bought Pro ($21.95, 6 months of email support & updates), your email address stays in the database for 6 months.
If you bought Extended Pro ($34.95, 12 months of email support & updates) then your email address stays in the database for a year.
After that, your email address is removed from the database & you can't download free updates any more.
If you paid a scam site for Pro then you won't ever be able to update from the official site.
After you bought Pro, you would have got an email from LW with a link to your Pro personal download page. Have a look through your emails & see if you can find it.
If you bought from the official site, LW will send you an email telling you when your Pro's about to expire