I upgraded from Freelance to Freelance Plus and activated the second PC with the new key without deactivating the license on the first PC. As a result, my first PC is activated with the license key for the Freelance version and second PC with the Freelance Plus version (I've found out the upgrade process belatedly). 

I was using the first PC without a problem but when I updated the second PC, the following error message appeared and couldn't open files. 

As I tried to deactivate the first PC, the error message said the following and couldn't deactivate.

Deactivation on my second PC worked well.

How do I properly set up two PCs at this point?