There is the possibility for every product and category to identify the keywords that will be present when a page is visited. To make that entry easier by way of mass population, EP4 offers that capability. The alternative is to allow Zen Cart to determine what keywords are presented or to manually enter them through the admin.
Thing is though as far as I can see in the EP4 code, with a proper installation of Zen Cart followed by a proper installation of EP4, there is no reason that the catalog side meta_tags.php file should even be accessed. So I'm not sure why the above error even happened from the admin side...
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