Mac Automator and Rscript

I put the following line in Mac Automator in a Run Shell Script (shell: /bin/bash)
	"Rscript --vanilla ~/Dropbox/Foo.R"

and get this error: Run Shell Script Failed ?1 error; Loading required package Defaults

I put that same line in a terminal and it runs perfectly fine.  Ditto for running the R file in Rstudio.

I can't get any more detail on the error.

What am I doing wrong in the Automator?

Thx,
John