There can be a couple of reasons for this.
One is when you purchased the full version of CC3 you left the trial version installed. What you need to do in this case is uninstall the trial version and install the full version.
The other possible issue is that you are using trial content or derivative content that requires other products to be installed. When this happens you will see a watermark on the screen. If you think this may be problem, but you have purchased all the content, then try going to Help > Activate Purchased Items.
Peter
Forum Administrator
www.reallusion.com