If you get a message ``Your authorization code has expired.''
You can simply get a new authorization code. 

Your new code will be valid for one year from the date you
obtain it.  You'll need to go through the same process next
year, but by then there will almost certainly be a newer 
version of Stimulate to download anyways.

The purpose of the authorization expiration is that we want
to keep a track of the number of sites actually using
Stimulate on an on-going basis.