Does the Craft config var "cache" exist?
I don't believe this is a valid configuration value. You will use the cache as a tag in your twig files:

{% cache %}
    {% for element in entry.hugeField %}
        {{ element.nestedAsset.first().url }}
    {% endfor %}
{% endcache %}


The cache is most effective at nested queries in matrix fields or asset fields or category fields. Do not use the cache for plain text fields or those that can be accessed in linear time.

I would just delete that line from your config.php