OpenSAML user discussion

Hi all,

I'm facing a strange problem. I'm trying to send a SAMLResponse (SAML 1.1) to 
an AssertionConsumerService but when validating the signature, he throws this 
error : 
SAMLSignedObject.verify() failed to validate signature value

Apparently there can be 2 reasons to this error : 
1) The certificate contained in the <ds:X509Certificate> element is not the 
same as the one used to sign the assertion.
2) The assertion changed AFTER its signature.

I don't think that the second reason is the right one.
So I want to show you the code I used to create the Credential and the code 
used to sign. Maybe you will see some mistake I did.

Here the code that creates the Credential : 
private BasicX509Credential buildCredential(String keyStorePwd, File 
keyStoreFile, String entityId, String alias, String password)
                        throws Exception {
                FileInputStream keyStoreFis = new 
FileInputStream(keyStoreFile);
                KeyStore keyStore = KeyStore.getInstance("JKS");
                keyStore.load(keyStoreFis, keyStorePwd.toCharArray());
                X509Certificate x509Certificate = 
(java.security.cert.X509Certificate) keyStore.getCertificate(alias);
                java.security.Key key = keyStore.getKey(alias, 
password.toCharArray());
                BasicX509Credential credential = new BasicX509Credential();
                credential.setEntityCertificate(x509Certificate);
                List<X509CRL> crls = new ArrayList<X509CRL>();
                credential.setCRLs(crls);
                credential.setEntityId(entityId);
                credential.setPrivateKey((PrivateKey)key);
                credential.setPublicKey(x509Certificate.getPublicKey());
                credential.getKeyNames().add(alias);
                return credential;
        }

And here is the code using this credential to create the signature : 
private Signature buildSignature(BasicX509Credential credential,String 
keyInfoId, String signatureAlgo, String signatureCanonicalAlgo) throws 
SecurityException, CertificateEncodingException {

                Signature signature = samlSignatureBuilder.buildObject();
                signature.setSigningCredential(credential);
                signature.setSignatureAlgorithm(signatureAlgo);
                
signature.setCanonicalizationAlgorithm(signatureCanonicalAlgo);
                NamedKeyInfoGeneratorManager namedKeyInfoGeneratorManager = 
securityConfiguration.getKeyInfoGeneratorManager();
                KeyInfoGeneratorManager keyInfoGeneratorManager =  
namedKeyInfoGeneratorManager.getDefaultManager();
                KeyInfoGeneratorFactory keyInfoGeneratorFactory =  
keyInfoGeneratorManager.getFactory(credential);
                KeyInfoGenerator keyInfoGenerator = 
keyInfoGeneratorFactory.newInstance();
                KeyInfo keyInfo = keyInfoGenerator.generate(credential);
                signature.setKeyInfo(keyInfo);
                
                return signature;
        }

Do you see any error or mistake in that code? I want to assure me that the 
used certificate for signing is the same that the one in the 
<ds:X509Certificate>.
Don't hesitate to ask me more informations, if you need.
Thanks in advance!