Actually, maybe this bug is the problem!
If I understand correctly (and I may not), parts of the R Cairo interface (or maybe the whole thing) are packaged with R, which is why you often don't need to actually install the Cairo R package just to use Cairo with plots.
That said, you could try running install.packages('Cairo') and seeing if that does the trick. (Or, if it doesn't, maybe install.packages('Cairo', type = 'source').