The error made by PNW was twofold. First, PNW erred in judging Leithart's views "to be not out of accord with the fundamentals of our system of doctrine." Second, PNW also erred in not finding a strong presumption of guilt that some of the views of Leithart are "out of accord with the fundamentals of the system of doctrine taught in the Westminster Standards."(source)
As you may be aware, Leithart is one of the signers of the Federal Vision Joint Statement. The expectation is that if Leithart continues to maintain the same positions and continues to remain in the PCA he will come under discipline.