Error in twitterR package

Hi,
I am trying to use twitter package. I got? below error?while authentication.

setup_twitter_oauth(api_key,api_secret,access_token, access_token_secret)

[1] "Using direct authentication"
Error in check_twitter_oauth() : OAuth authentication error:
This most likely means that you have incorrectly called setup_twitter_oauth()'
I am using windows machine. Please find below code and software details;
library("twitteR")
library(httr)
library(ROAuth)
download.file(url="http://curl.haxx.se/ca/cacert.pem", destfile="cacert.pem")
api_key? <-"xxx"
api_secret? <- "xxx"
access_token? <- " xxx"
access_token_secret? <- "xxx"
setup_twitter_oauth(api_key,api_secret,access_token, access_token_secret)
R version : Ri386 3.3.0R studio:??0.99.902?
Thanks,Seema