ruby on rails - Twitter gem update_with_media method is returning "could not authenticate you" -

i'm using twitter gem automate tweets. since want tweets include image i'm using "update_with_media" method, so:

def tweet     client = twitter::rest::client.new |config|       config.consumer_key        = "my consumer key"       config.consumer_secret     = "my consumer secret"       config.access_token        = "my access token"       config.access_token_secret = "my secret access token"     end      client.update_with_media("some text \n ", open(self.image_url))   end 

the error being returned twitter states "cannot authenticate you". credentials i'm using above correct though, posts tweet without error when use update method (tweet w/out image). have experience dealing or similar issue? thanks.