SonarQube no code coverage with OpenCover

I'm using SonarQube 5.1.1, sonar-runner 2.4, the latest version of the C# plugin for SonarQube and Opencover for my code coverage.

I run sonar-runner on my computer, it analyse the source code and send it to sonar but the code coverage is always set as "-".

Here is a part of my sonar-project.properties file :

sonar.sources=source
sonar.exclusions=source/project/UnitTests/**, source/project/InstallerUnitTests/**, source/addin/UnitTests/**
sonar.tests=source/project/UnitTests, source/project/InstallerUnitTests, source/addin/UnitTests

# Encoding of the source code. Default is default system encoding
sonar.sourceEncoding=UTF-8

sonar.language=cs

# Enable the Visual Studio bootstrapper
sonar.visualstudio.enable=true

sonar.gallio.coverage.tool=OpenCover 
sonar.cs.opencover.reportsPaths=source/build/opencover/Shortcuts.Coverage.xml

Can anyone help me to understand why SonarQube don't display the code coverage ?