Stationary sets and infinitary logic

Let K-lambda(0) be the class of structures [lambda, < A], where A subset of or equal to lambda is disjoint from a club, and let K-lambda(1) be the class of structures [lambda, <, A],where A subset of or equal to lambda contains a club. We prove that if lambda = lambda(<k) is regular, then no sentance of Llambda+kappa separates K-lambda(0) and K-lambda(1). On the other hand, we prove that if lambda = mu(+), mu = mu(<mu), and a I forcing axiom holds (and N-1(L) = N-1 if mu = N-0), then there is a sentance of L-lambda lambda which separates K-lambda(0) and K-lambda(1).