Error when trying upgrade Multiplicity from standard to pro

I get the following error when trying to enter my email address and serial number:

Your ThinkDesk registration could not be found.   If you are in need of assistance please contact [email protected].

After following the link to the upgrade stie here: https://www.stardock.com/products/multiplicity/purchase.asp

I checked and double checked that my email and serial number are correct.

I also removed the dashes in the serial number just in case. When I emailed [email protected] I recieved an undeliverable response.

Has anyone had any touble like this?

Thanks