  Several recent possible counterexamples to the Chronology Protection
Conjecture are critically examined. The ``adapted'' Rindler vacuum state
constructed by Li and Gott for a conformal scalar field in Misner space is
extended to nonconformally coupled and self-interacting scalar fields. For
these fields, the vacuum stress-energy always diverges on the chronology
horizons. The divergence of the vacuum stress-energy on Misner space chronology
horizons cannot be generally avoided by choosing a Rindler-type vacuum state.
