Salesforce Authentication Failing

I am trying to use OAuth authentication to get the Salesforce training Authentication Token, so I referred wiki docs, but after getting authorization code, when I make a Post request with 5 required parameters, I'm getting following exception

{"error":"invalid_grant","error_description":"auth entication failure"} CODE 400
JSON = {"error":"invalid_grant","error_description":"auth entication failure"}
which is I guess a bad request.

PostMethod post = new PostMethod("https://login.salesforce.com/services/oauth2/token");
post.addParameter("code",##############);
post.addParameter("grant_type","authorization_code ");
post.addParameter("redirect_uri","################ #");
post.addParameter("client_id",this.client_id);
post.addParameter("client_secret",this.client_secr et);
httpclient.executeMethod(post);
String responseBody = post.getResponseBodyAsString();
System.out.println(responseBody+" CODE "+post.getStatusCode());
Kindly reply, if exception known?