OK, I'm glad to hear it fixed itself after restarting! If something like that happens again, you can "force" X-Plane to bring up the product key authorization box by deleting a preference file.
On OS X it’s in users/(username)/Library/Preferences/ -> delete file X-Plane_drm.prf
On Windows the file will be in the user local app data folder, e.g. C:\Users\nnnn\AppData\Local\.