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Got answer from support today and this worked for. Basically you need to cleanly uninstall Parallels first and then reinstall it. After that the...
I'm having the same problem. Got my key from parallels.com > My Account > My Registered Products and copy-pasted the key. When I updated from PD 3...
I'm having the same problem - I've got the activation key from parallels.com > My Account > My Registered Product and copy-pasted it.