Here are the verses Proverbs 26:4 and Proverbs 26:5:
I don't regard this as a problem at all - it's what I would call "contradiction for rhetorical effect". The fact that the two verses are right next to each other indicates that the contradiction is deliberate. The intended meaning appears to be: Arguing with a fool: you're damned if you do, and you're damned if you don't.