The reason why the Admin button wasn't showing was that I had the window set too small... Well, you live, sometimes you learn.
The hints given here by AtinLango and aysiu were helpful, thank you guys (?). Especially the kuser proved to be valuable, since my userconfig is broken somehow. Every time I use it, it makes it impossible to unlock locked sessions (described here:
http://www.linuxquestions.org/questi...d.php?t=424674 ). And in addition it cannot edit some of my users, but kuser seems to do the job.