The error message text is not explicit, but the error number 15013 implies that you are trying to activate (again) an already activated product. This error occurs, when you enter the license key of a currently activated license via the license key activation dialog again (normally used for full version activation during trial period).

Note:Your application is already activated and working. This step is not necessary. The startup dialog message should already show, that a trial version is activated and the about dialog should display trial version. Also,  you should be able to save and print with his version.