Il y a ca dans Launcher Log :
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:387) ~[?:1.8.0_25]
at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:292) ~[?:1.8.0_25]
at sun.security.validator.Validator.validate(Validator.java:260) ~[?:1.8.0_25]
at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:324) ~[?:1.8.0_25]
at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:229) ~[?:1.8.0_25]
at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:124) ~[?:1.8.0_25]
at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1453) ~[?:1.8.0_25]
at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:212) ~[?:1.8.0_25]
at sun.security.ssl.Handshaker.processLoop(Handshaker.java:936) ~[?:1.8.0_25]
at sun.security.ssl.Handshaker.process_record(Handshaker.java:871) ~[?:1.8.0_25]
at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1043) ~[?:1.8.0_25]
at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1343) ~[?:1.8.0_25]
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1371) ~[?:1.8.0_25]
at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1355) ~[?:1.8.0_25]
at sun.net.
www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:563) ~[?:1.8.0_25]
at sun.net.
www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185) ~[?:1.8.0_25]
at sun.net.
www.protocol.http.HttpURLConnection.getOutputStream0(HttpURLConnection.java:1281) ~[?:1.8.0_25]
at sun.net.
www.protocol.http.HttpURLConnection.getOutputStream(HttpURLConnection.java:1256) ~[?:1.8.0_25]
at sun.net.
www.protocol.https.HttpsURLConnectionImpl.getOutputStream(HttpsURLConnectionImpl.java:250) ~[?:1.8.0_25]
at com.mojang.authlib.HttpAuthenticationService.performPostRequest(HttpAuthenticationService.java:73) ~[launcher.jar:1.6.11]
at com.mojang.authlib.yggdrasil.YggdrasilAuthenticationService.makeRequest(YggdrasilAuthenticationService.java:54) ~[launcher.jar:1.6.11]
... 9 more