For admins (and not superuser) you need to stop the server, download murmur.sqlite, open it with sqlitebrowser and manually add an admin.
I made a tutorial including a video there :
http://www.roxservers.com/index.php?fuse=knowledgebase&view=KB_viewArticle&articleId=8&public=1
If you talk about superadmin powers you may have missed something from my first post, try to type the commands manually instead of executing the bat.
It works on windows 2003 std 64 bits, not tested on another environment.
PS : I had to enable file manager to let customers download and edit murmur.sqlite (originally disabled in my first config).