Nock's advice is excellent... all the more so, since there's now a good translation of Proclus' text! This is one of those places where I really recommend against Thomas Taylor's version, through no fault of Taylor's. In his day, the manuscript of Proclus' three little treatises on providence and evil was in horrific shape, to the point where Taylor himself (as I recall) acknowledges having to skip over some fairly large sections because the received text was utterly incomprehensible, and was only able even to attempt a translation of two out of the three treatises. Since then, new materials have been found and edited that put the text on a much more coherent footing. The translation of Proclus' On the Existence of Evils by Jan Opsomer and Carlos Steel (2003), which draws on those new discoveries, is excellent.

For "lack of mind," you might consider my comment below about "missing the mark" as a starting point. Mind (or intellect) is the metaphysical principle that stands below being and prior to soul in the basic Platonic metaphysics as given by Proclus et al. It's that which eternally and essentially knows the transcendent Ideas as such, and knows material particulars only insofar as those particulars are already pre-existing in their paradigms.

So, given that there are only paradigms of goods and not of evils (per my comment below), and given that intellect only knows ideas/paradigms, then it follows that intellect can only know goods. And it likewise follows that anything which knows evils must be other than intellect/mind.