I just purchased an additional license ( annual payment ), because I run SONAR on 3 PCs.
CCC welcomed me by name, shows a serial number, but sonar runs in DEMO mode.
When Internet fails on any PC I fall immediately in DEMO mode.
When I buy a licence - I am in DEMO mode.
Each time I start SONAR my account is checked over the internet. When internet is pluged out, SONAR needs more than a minute to start (searching the internet connection) - and falls in DEMO mode.
"Please contact support - Error Number: 40,0"
 
What should I do to be able to work?
I cannot call the suport by phone, because I write with Google's German / English translater.
 
 

If you cannot phone, then email support is the alternative. The activation support page is here http://www.cakewalk.com/Support/Email/Activation. The email form is at the bottom of the page.

There was no reason to buy another licence.  You should be able to install Sonar on every single computer you own, as long as you only use one at at time.  (though you can only have AD and Melodyne active on two computers at any one time).  
 
I'd contact Cakewalk and see if they will switch out your purchase into a very long membership extension assuming you do not need those two programs to always have an activation...and even if you do, it might be cheaper to buy additional licences for those.  

I use Sonar Platinum parallel on three PCs at the "same" time (because we are digitazing tapes and vinyl).
The support says that it's taking to long to find the auth file.
At the moment it works and the new license was suddenly accepted after several attempts.
But I experience problems repeatedly.
The problem is currently away - but not solved.