Deskscapes 11 not recognising serial number

I just bought the update to Deskscapes 11.

Installed it.

Sadly it wouldn't allow me to keep Deskscapes 10 installed at the same time, it gave me no choice to do that as it presented me with a rather odd looking screen pop-up.

It's either Cancel (so no new version to try out) or OK (and it automatically uninstalled the working version I have). 

Does the customer not get a choice of what they'd like to do?

If it's a beta version (which Deskscapes 11 is) I prefer to install alongside a working previous version to see how the new one behaves before stepping up a version. 

Anyway, it installed and so I tried to activate it with the number you'd supplied at purchase. Copied and pasted the serial number from the purchase confirmation page, and get 'An invalid product key was entered'

Back, and enter the serial number, this time by hand and get the same message.

I follow the instructions on that message, and it fails again. I did as requested 'click here to have your key emailed to you' 

Email arrives with EXACTLY the same serial number I'd copied from purchase screen. 

I try to activate the new installation again, using both copy and paste of the serial from the email, and entering details manually.

Same problem each time. 

Stardock,  how the heck can I activate the software I purchased from you when it won't recognise the serial number you have supplied??

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UPDATE:  Re-ran the installer and this time it allowed activation.  Note: this time I wasn't given a choice of what drive I could install it to. Deskscapes 10 was installed on D: