Sonarqube produces build error using the new Team Foundation Build - iis

Question

I have a problem integrating Sonarqube in the Build process with the Build-Tasks in Visualstudio Online.
My Konfiguration:
SonarQube 5.2 with LDAP using the Active Directory to Login in SonarQube
I use a reverse Proxy (IIS 8.5) as recommended on the Sonarqube homepage to access Sonarqube over a public Endpoint. This is nessacry because I use a public Build-Server, so that he can reach the Sonarqube Server.
I have no problem accessing Sonarqube over the Web. I got prompt for the credentials. I can login with my domainuser and browse without any Problems. If I use the private Endpoint I got login automatically. It seems to me that some informations for the login got lost over the reversed proxy.
Now the actual problem:
If I start a Build as mentioned bevor, I get the folowing error while the "End-Analyses" Task. The error occurs running the sonarrunner.
ERROR: Error during Sonar runner execution
org.sonar.runner.kevinsawicki.HttpRequest$HttpRequestException: java.net.SocketException: Connection reset
at org.sonar.runner.kevinsawicki.HttpRequest.code(HttpRequest.java:1392)
at org.sonar.runner.kevinsawicki.HttpRequest.ok(HttpRequest.java:1417)
at org.sonar.runner.impl.ServerConnection.downloadString(ServerConnection.java:93)
at org.sonar.runner.impl.ServerVersion.downloadVersion(ServerVersion.java:47)
at org.sonar.runner.impl.ServerVersion.version(ServerVersion.java:38)
at org.sonar.runner.impl.ServerVersion.is37Compatible(ServerVersion.java:58)
at org.sonar.runner.impl.JarDownloader.checkVersionAndDownload(JarDownloader.java:36)
at org.sonar.runner.impl.BatchLauncher$1.run(BatchLauncher.java:71)
at java.security.AccessController.doPrivileged(Native Method)
at org.sonar.runner.impl.BatchLauncher.doExecute(BatchLauncher.java:69)
at org.sonar.runner.impl.BatchLauncher.execute(BatchLauncher.java:50)
at org.sonar.runner.api.EmbeddedRunner.doExecute(EmbeddedRunner.java:102)
at org.sonar.runner.api.Runner.execute(Runner.java:100)
at org.sonar.runner.Main.executeTask(Main.java:70)
at org.sonar.runner.Main.execute(Main.java:59)
at org.sonar.runner.Main.main(Main.java:53)
Caused by: java.net.SocketException: Connection reset
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection$10.run(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection$10.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.net.www.protocol.http.HttpURLConnection.getChainedException(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at java.net.HttpURLConnection.getResponseCode(Unknown Source)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(Unknown Source)
at org.sonar.runner.kevinsawicki.HttpRequest.code(HttpRequest.java:1390)
... 15 more
Caused by: java.net.SocketException: Connection reset
at java.net.SocketInputStream.read(Unknown Source)
at java.net.SocketInputStream.read(Unknown Source)
at sun.security.ssl.InputRecord.readFully(Unknown Source)
at sun.security.ssl.InputRecord.read(Unknown Source)
at sun.security.ssl.SSLSocketImpl.readRecord(Unknown Source)
at sun.security.ssl.SSLSocketImpl.performInitialHandshake(Unknown Source)
at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
at sun.security.ssl.SSLSocketImpl.startHandshake(Unknown Source)
at sun.net.www.protocol.https.HttpsClient.afterConnect(Unknown Source)
at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getInputStream(Unknown Source)
at sun.net.www.protocol.http.HttpURLConnection.getHeaderField(Unknown Source)
at sun.net.www.protocol.https.HttpsURLConnectionImpl.getHeaderField(Unknown Source)
at org.sonar.runner.kevinsawicki.HttpRequest.header(HttpRequest.java:1903)
at org.sonar.runner.kevinsawicki.HttpRequest.contentType(HttpRequest.java:2308)
at org.sonar.runner.impl.ServerConnection.downloadString(ServerConnection.java:89)
... 13 more
ERROR:
ERROR: Re-run SonarQube Runner using the -X switch to enable full debug logging.
The sonar-runner did not complete successfully
I reserached a lot but can't find any solution for my problem. Can Someone help?
Edit:
If I use the the private Endpoint to integrate Sonarqube in the Build there are now Problems. in this case The Sonarqube Analyses works fine. But I need to get this work over the public endpoint using the reverse proxy redirecting to the local machine.