error with df.read.csv

Hi!
I followed you read.me, everything works fine until I enter:
my_data <- db.read.csv(dropbox_credential, "myfile.csv", header=TRUE)

and I get this:

Error: File or Folder does not exist
HTTP/1.1 200 OK>

and my R prompt is gone

The file is the folder and I am working on a Mac and R version 2.15.2

Any suggestions?
thank you