  We are concerned with how regular initial data have to be to ensure local
existence for Einstein's equations in wave coordinates. Klainerman-Rodnianski
and Smith-Tataru showed that there in general is local existence for data in
Sobolev spaces H^s with regularity s>2. We give an example of data in Sobolev
spaces with regularity s=2 for which there is no local solution in this space.
