The main element of logical positivism was verificationism. This led to the attitude, that only propositions proven by verification are worth to discuss in philosophy. So metaphysics and ontology had to be ignored according to Vienna circle as they cannot be proved by objective methods.

The problem with this view, articulated mainly by Karl Popper, was that for verification of a proposition, one needs absolute truths on which he can base the verification. This is known as the Münchhausen Trilemma. Popper as founder of falsificationism in his critical rationalism, a kind of historic fallibilism, stated that there is nothing we can be 100% sure about, there is ALWAYS the chance of being wrong. We can only falsify current knowledge and develop more exact, consistent and coherent theories. This is the current paradigma believed by most natural scientists.

I foundy only a german diagram of this famous trilemma, use translation if it is not self-explaining