What is [sic] unconditional love's greatest errors?
I disagree with your premise. There is no issue with loving unconditionally. There is issue in being stupid and letting yourself be manipulated because of your love.
For instance, a child needs limits. If a parent doesn't provide them, he's not loving his child, he's abdicating his responsibility. Do you have any idea what it takes to not cave to a child at certain times? But I'd argue you are not loving your child if you do.
How about not enabling a junkie if that's your m.o? Or holding the hand of someone who's dying? Or letting a person make his own mistakes? And being ready to not be right about it?
So yes, love unconditionally, but be wise, be straight, be forthright, be responsible for your word.