I had the same problem and it was discussed in a forum thread last week or so. It was caused by the "upgrade offer" from the third party vendor, tied into a licensing key check. It took a couple hours out of my life, trying to read the documentation and watch training videos to see what was wrong. If this happens to you, you need to find the extra window that is open and re-register the software.
Cakewalk seems to be "licensing" more and more, for instance Melodyne and Addictive. This is just fine, except the other vendors have all kinds of paranoia about security that turns into annoying problems for us Sonar users. Not to mention the very annoying upgrade "offers" Celemony keeps popping into my life.
I frankly do not like Melodyne, its just too complicated. I suppose that the nature of what it does is complicated, and that is the reason for it's lack of approachability. But the fact is that for me it is going on the back burner because I don't feel like watching the training videos over and over just to do what I have been doing in V-Vocal and Autotune for the last 10 years.
Plus the tone of the Celemony training videos is so condescending that I really loose my enthusiasm.