No ggplot2 graphs are working: "Error in y[setdiff(names(y), names(x))] : object of type 'closure' is not subsettable"

Question

I'm new to R, and struggling to get ggplot2 to reliably work. Even simple code snippets that have been reproduced elsewhere are failing on my machine.

This:

library(ggplot2)
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length)) + geom_point()

Gives me:

Error in y[setdiff(names(y), names(x))] : object of type 'closure' is not subsettable

Importantly, this was working yesterday. I can't think of anything that changed. Now it's not.

I've reinstalled R, Rstudio and ggplot2 to no avail. My guess is that there's a versioning problem somewhere, but am not sure.

Thanks for any help.

UPDATE

Here's the output from sessioninfo():

R version 3.3.0 (2016-05-03)
Platform: x86_64-apple-darwin13.4.0 (64-bit)
Running under: OS X 10.10.5 (Yosemite)

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] ggrepel_0.5   scales_0.4.0  ggplot2_2.1.0

loaded via a namespace (and not attached):
[1] labeling_0.3     colorspace_1.2-6 plyr_1.8.3       tools_3.3.0             
gtable_0.2.0    
[6] Rcpp_0.12.5      grid_3.3.0       munsell_0.4.3   

Answer 1

I can reproduce this error message if I set an invalid default theme. For example:

library(ggplot2)
theme_set(theme_bw) # improper usage of theme_set, should be theme_set(theme_bw())
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length)) + geom_point()

gives me the error

Error in y[setdiff(names(y), names(x))] : 
object of type 'closure' is not subsettable

but

library(ggplot2)
theme_set(theme_bw()) # have now fixed theme_bw
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length)) + geom_point()

works fine.