The FitNesse Hudson Plugin version 1.4 allows Hudson to store the results in a results.xml file.
After running all the tests, Hudson can also publish these Fitnesse results.

This is the problem that we have when the Hudson job is done:

Xml results saved as windows-1252 to D:\hudson\workspace\FitNesse 8332 BE Full\results\test.xml
Reading results as windows-1252 from D:\hudson\workspace\FitNesse 8332 BE Full\results\test.xml
Parsing results...
Got results: null
java.lang.NullPointerException
at hudson.plugins.fitnesse.FitnesseResults.getFailCount(FitnesseResults.java:98)
at hudson.tasks.test.TestResult.getBuildResult(TestResult.java:93)
at hudson.plugins.fitnesse.FitnesseResultsRecorder.perform(FitnesseResultsRecorder.java:64)
at hudson.tasks.BuildStepMonitor$3.perform(BuildStepMonitor.java:36)
at hudson.model.AbstractBuild$AbstractRunner.perform(AbstractBuild.java:602)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:581)
at hudson.model.AbstractBuild$AbstractRunner.performAllBuildSteps(AbstractBuild.java:559)
at hudson.model.Build$RunnerImpl.post2(Build.java:158)
at hudson.model.AbstractBuild$AbstractRunner.post(AbstractBuild.java:529)
at hudson.model.Run.run(Run.java:1278)
at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:46)
at hudson.model.ResourceController.execute(ResourceController.java:88)
at hudson.model.Executor.run(Executor.java:124)
Email was triggered for: Failure
Sending email for trigger: Failure

We did some investigation:
The ending tag </testResults> is missing at the end of the results.xml file and the FitNesse test results are written 2 times to the results.xml file.
Inside the results.xml file, we also see that the xml-header <?xml version="1.0"?> is written twice.
This causes the XML file to be invalid xml.