Since I have added the clocker plugin to my cppunit code(It is a cppunit plugin which permit to have the time execution, available into the samples of the cppunit archive), xunit don't reconize the format of the cppunit report.
In fact, jenkins says that :
[xUnit] [INFO] - Starting to record.
[xUnit] [INFO] - Processing CppUnit-1.12.1 (default)
[xUnit] [INFO] - [CppUnit-1.12.1 (default)] - 1 test report file(s) were found with the pattern 'report/cppunit-report.xml' relative to '/home/nicolas/jenkins/workspace/ProjectA' for the testing framework 'CppUnit-1.12.1 (default)'.
[xUnit] [ERROR] - The result file '/home/nicolas/jenkins/workspace/ProjectA/report/cppunit-report.xml' for the metric 'CppUnit' is not valid. The result file has been skipped.
[xUnit] [INFO] - Setting the build status to FAILURE
[xUnit] [INFO] - Stopping recording.
Build step 'Publish xUnit test result report' changed build result to FAILURE