If you have recently restored your Mac computer with a Time Machine Backup then most likely, especially if you are restoring to another computer, you will have issues activating the plug-in. This is because old license files are carried over to the new computer. These old files must be deleted and plugin should be re-installed to solve this issue.
You need to delete the .GridCalculator folder found in Applications/.GridCalculator (this folder is hidden). This can be done manually but starting from Grid Calculator Pro Edition CC 2017 version, in Activator there is a new menu added: Activator CC 2017 > Delete Activation Files. This will delete the .GridCalculator folder. Please note that you will need to reinstall the plug-in for the required files to be added to the system again in order to activate and run the plug-in.