While pruning a lattice wrt posterior probs with this command: lattice-tool -in-lattice lattice -read-htk -out-lattice - -write-htk -posterior-prune 1.0e-1 I got this error Lattice::computeForwardBackward: warning: called with unreachable nodes If I decrease pruning threshold this error disappears. Who can help me? best regards Nicola