I've just upgraded to version 11 and I wonder whether I'm still authorized to use version 10 on my other computer.
I see I can no longer log into my account on DOpus page using my previous serial (the new one works) so I suspect my serial for version 10 is no longer active.
Can anyone comment on that? Thanks for clarifying!
If you upgrade a licence then you still end up with the same number of licences, not an extra copy.
You'd only get an extra copy if you bought a whole new licence, or added additional ones at the same time as upgrading.
That's clear (and fair)! Thank you, leo!
They spell this out on the page with the Upgrade Quotation:
[quote="michaelkenward"]They spell this out on the page with the Upgrade Quotation:
I saw that. What, exactly, does it mean? That as soon as I purchase a new license, Opus 10 stops working.
What if I install 11 and then want to, probably temporarily, go back to 10? If I reinstall 10, will it refuse to accept my previous certificate?
Your v10-license does not expire, you're just not allowed to use it parallel with the upgraded one.
When you upgrade your original licence is cancelled, however Opus 10 will accept Opus 11 certificates so you can use your upgraded licence with Opus 10 if desired.
...yesterday I upgraded my sys and restored an image where v10 was installed, and the old license was still accepted.
But another question: What about using DO in a VM? E.g. MS' license policy requires one license per VM (alltough a VM still needs a licensed host on same hardware).
"On a machine for which you have a license, you may install the software on multiple operating systems or virtual machines for use by one user at the same time."
Who reads the small print... (who read the complete DO-manual?) 
. Thanks, Leo.
Who reads anything? 
Did you write something?