Scribe + Xing => Invalid OAuth signature - oauth

Question

I'm trying to use scribe with XING and I'm always getting following answer:
Can't extract token and secret from this: '{"message":"Invalid OAuth signature","error_name":"INVALID_OAUTH_SIGNATURE"}'
I have a working login process, get back an oauth_token and an oauth_verifier and tried to to change the defaultly selected HMACSha1 Singature with a PlainText signature, but I'll always get the above mentioned result...
Any ideas on why this happens?
Using the default DefaultApi10a and XingApi from scribe always fails at the above mentioned step...
EDIT - Code
// Creating the service
// callback is needed to stop redirecting in the webview
OAuthService service = new ServiceBuilder()
.provider(XingApi.class)
.apiKey(apiKey)
.apiSecret(apiSecret)
.callback("http://www.xing.com")
.build();
Step 1: get request token + auth url
RequestToken requestToken = service.getRequestToken();
String authUrl = service.getAuthorizationUrl(requestToken );
Step 2: load the auth url in a webview + check the redirect url and cancel redirection based on callback
for example, redirection url look like following: http://www.xing.com?oauth_token=a2191ab84c9e0f85cf0c&oauth_verifier=4978
Step 3: extract oauth_token + oauth_verifier from returned url
String oauthToken = ...; // a2191ab84c9e0f85cf0c in the example
String oauthVerifier = ...; // 4978 in the example
Step 4: get access token => this fails
Token requestToken = new Token(oauthToken, oauthVerifier); // reusing the request token from above results in invalid request token answer from xing!
Verifier v = new Verifier(oauthVerifier);
Token accessToken = service.getAccessToken(requestToken, v);

Answer 1

Remove:
Token requestToken = new Token(oauthToken, oauthVerifier); // reusing the request token from above results in invalid request token answer from xing!
line from step 4.
You have to keep request token to retrieve access token using it and verifier (4 digits PIN) from Xing.
EDIT - code added:
OAuth10aService service = new ServiceBuilder()
.apiKey("44a4f9c1a9daa88f4da2")
.apiSecret("2fc8ca373dab772acc4de7ce22718f8fced6919c")
.callback("https://redirect.example.com")
.build(XingApi.instance());
final Token requestToken = service.getRequestToken();
System.out.println(service.getAuthorizationUrl(requestToken));
System.out.println("Paste the verifier here");
System.out.print(">>");
Scanner in = new Scanner(System.in);
Verifier verifier = new Verifier(in.nextLine());
System.out.println();
in.close();
// Trade the Request Token and Verfier for the Access Token
Token accessToken = service.getAccessToken(requestToken, verifier);
System.out.println("Got the Access Token! " + accessToken);