I get no errors for that plot. Scatterplot as one would expect.
> sessionInfo()
R version 2.15.2 (2012-10-26)
Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
locale:
[1] en_US.UTF-8/en_US.UTF-8/en_US.UTF-8/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] scales_0.2.3 ggplot2_0.9.3
loaded via a namespace (and not attached):
[1] colorspace_1.2-0 dichromat_1.2-4 digest_0.6.0 grid_2.15.2
[5] gtable_0.1.2 labeling_0.1 MASS_7.3-22 munsell_0.4
[9] plyr_1.8 proto_0.3-9.2 RColorBrewer_1.0-5 reshape2_1.2.2
[13] stringr_0.6.2