Perhaps the prefs file is corrupted. Start by resetting the prefs and seeing if that fixes things:
1) restart IP Scanner while holding down the option and command keys and choose the option to reset the prefs (save your customizations when prompted, if you have any)
2) restart the app and then re-import your saved customizations
3) re-enter your license info and click the ‘Register’ button
If this does not work, please send us a screenshot of what you see in registration window.