This may be caused by a corrupt installation.
Please uninstall and then reinstall the plugin.
If the issue persists check that you have the correct licence file (.dat file) in this folder:
C:\ProgramData\MasteringTheMix
If the file is there, right click on it, choose Properties and then click the Security tab and highlight the Users group. You should only see Read & execute and Read ticked. Similar to below.
