  The proof of the failure of the ladder approximation to QCD is given in
manifestly gauge-invariant way. This proof is valid for the full gluon
propagator and for all types of quarks. The summation of the ladder diagrams
within the Schwinger-Dyson integral equation for the quark-gluon vertex, on
account of the corresponding Slavnov-Taylor identity, provides an additional
constraint on the quark Schwinger-Dyson equation itself in the ladder
approximation. It requires that there is neither running nor current quark
masses in the ladder approximation. Thus, all the results based on the
nontrivial (analytical or numerical) solutions to the quark Schwinger-Dyson
equation in the ladder approximation should be reconsidered, and its use in the
whole energy/momentum range should be abandoned.
