1. Make sure you are entering the appropriate license key in the right product registration window. For example, do not try to enter a “SkyBox Studio” license key in “SkyBox VR Player” or a “FreeForm” license key in “FreeForm Pro”.
2: Make sure your license key is entered exactly. Best practise is to Mouse -> Right Click -> Copy the License Key then Mouse -> Right Click -> Paste the License Key in the appropriate field in the “Register” window.
3. You may have the plugin registered on too many computers to activate the license key one more time. In the Register Window. Deactivate All. Close the Register Window. Open and Activate again.
4. You may be trying to use an older serial number in a newer version of the plugin. You need to download an earlier version of the plugin that will work with your serial number. You have old/new installers in your mettle account: http://www.mettle.com/my-account/