Pro allows updates for six months, but after that it's time to pay again.
I'm guessing you used the cheque quite a while ago, since it's been almost two years since they gave up accepting cheques, IIRC.
Still, see if any of the contact info at
http://www.limewire.com/english/cont...pportpro.shtml will work. There is no phone support (makes sense with millions of users).
If not, time to pony up and keep supporting the project