Ggsave error "cannot open file"

Question

I run ggsave('plot.pdf')and get this error:

Error in grDevices::pdf(..., version = version) :
  cannot open file 'plot.pdf'

Even when I don't have plot.pdf open. I am working on NFS. If I go to the new file and then run ggsave again on the same path, it will overwrite the file successfully. However, if I open and close the file before running ggsave on the same path, I get the above error. Any thoughts on why this is happening?