I just installed the latest version of sonarqube on my server and did a test run on my project with the sonar-scanner executable. This works.
In the next step, i'm creating a new VSTS Build Definition with the existing SonarQube build steps.
When I trigger this build, it fails in the last step, after the report has been uploaded to my SonarQube server:
I don't know why this happens, because the sonar-scanner is working just fine. I'm using the same parameters in my MS Build step.
Looks like your VSTS task is pending completion of the Background Task on SonarQube server side, as per this log in your first screenshot:
Waiting on the sonarqube server to finish processing in order to determine the quality gate status
(note: this is a log from the VSTS task itself, not from the SonarQube Scanner which did finish successfully)
The problem is that the Background Task actually fails with an error as per your second screenshot. The failure corresponds to bug SONAR-8013 (fix to be released in upcoming SonarQube 6.1).