Odd. I just tried, and the lookup page at
http://sales.limewire.com/support/? worked fine.
I've had troubles in the past remembering which email address i had used, but eventually hit the right one.
Anyway, the Pro page usually switched to a link with a reminder that my Pro expired, and I just used the link from there to get it renewed.
Don't you still have the link to your old page?