I found that I got a javascript error when entering my registration key. Monique at the support desk advised that I might solve the problem by downloading the latest Java update from http://java.sun.com/javase/downloads/?intcmp=1281 and trying again. Unfortunately I had problems with this download although others might get it right.
So then Monique sent me the Java update in a zip file, I installed it, then uninstalled SeaGreen and reinstalled it (important), entered the registration key and it worked. (If you ask Monique nicely she might send it to you too)
Just in case others might have the same problem ...
Jen