Works fine for me: you probably have an old version.

> sessionInfo()
R version 2.7.0 (2008-04-22)
i386-pc-mingw32

locale:
LC_COLLATE=English_United Kingdom.1252;LC_CTYPE=English_United
Kingdom.1252;LC_MONETARY=English_United
Kingdom.1252;LC_NUMERIC=C;LC_TIME=English_United Kingdom.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] lme4_0.999375-22   Matrix_0.999375-11 lattice_0.17-12

loaded via a namespace (and not attached):
[1] grid_2.7.0

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