Exception in thread "main" com.sun.tools.attach.AgentLoadException: Agent JAR not found or no Agent-Class attribute
In the stack trace you can see in the path to the file leak detector jar, the space is being "percent-encoded" e.g. C:\Program%20Files\Jenkins...
Moving the Jenkins folder so that JENKINS_HOME did not have a space in it resolved the issue.
Response (stack trace) when attempting to activate the file leak detector is attached.