人間は普通ここに来れんのになあ I Know it means Humans Cannot Come here usually.
but doesn't 来られます Means can come Potential Form But 来れ Then ん Confuses me.
I would advise you to check out the Denshi Jisho entry for ん.
In this case, ん is an abbreviation of ぬ, which is a negative verb ending.
A good way to translate 来れん would be “can't come”.