[R-sig-ME] glmer warning "fixed-effect model matrix is rank deficient"

[Dan McCloy]

sessionInfo:
R version 3.1.0 (2014-04-10)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
LC_CTYPE=en_US.UTF-8
LC_NUMERIC=C
LC_TIME=en_US.UTF-8
LC_COLLATE=en_US.UTF-8
LC_MONETARY=en_US.UTF-8
LC_MESSAGES=en_US.UTF-8
LC_PAPER=en_US.UTF-8
LC_NAME=C
LC_ADDRESS=C
LC_TELEPHONE=C
LC_MEASUREMENT=en_US.UTF-8
LC_IDENTIFICATION=C

attached base packages:
stats
graphics
grDevices
utils
datasets
methods
base

other attached packages:
caret_6.0-24
ggplot2_0.9.3.1
lattice_0.20-29
zoo_1.7-11
lme4_1.1-6
Rcpp_0.11.1
Matrix_1.1-3

loaded via a namespace (and not attached):
car_2.0-20
codetools_0.2-8
colorspace_1.2-4
digest_0.6.4
foreach_1.4.2
grid_3.1.0
gtable_0.1.2
iterators_1.0.7
MASS_7.3-31
minqa_1.2.3
munsell_0.4.2
nlme_3.1-117
nnet_7.3-8
plyr_1.8.1
proto_0.3-10
RcppEigen_0.3.2.1.1 reshape2_1.4        scales_0.2.4
[19] splines_3.1.0       stringr_0.6.2       tools_3.1.0