BMUnit relies upon the API provided by the JVM Tools library class VirtualMachine to automatically locate the current Java process and load the Byteman agent before it runs BMUnit tests. On Windows method VirtualMachine.list() is used to locate all running JVMs and their associated processids (pids). A secondary API of VirtualMachine is used to identify which pid belongs current JVM.
VirtualMachine.list() appears not to be functioning correctly on Windows 7 as it returns no candidate JVMs. There does not appear to be any portable way to identify the current pid so this means BMUNit will be broken until the WIndows 7 implementation of VirtualMachine is fixed.
A workaround is available (See workarounds section of this JIRA).