For one of our projects we use the StyleCop plugin for SonarQube during the analysis. As you can see it was recently deprecated.
I successfully updated the instance used by this product to SonarQube 6.0, when I was told an exception was raised while building:
To make things worse, there are no workarounds or quick fixes to unblock it as you can see from here. The reason behind this is because it isn’t using the .NET Compiler Platform.
Long story short – the plugin is deprecated and it won’t work with SonarQube 6.0. You can either disable the plugin and keep SonarQube 6.0 running or revert back to SonarQube 5.6.1.