I just came across this post http://archicad-talk.graphisoft.com/viewtopic.php?t=24558
while browsing the Student Forum and had to chime in. This same thing happened to me yesterday. I couldn't place the user origin with shorcut keys(alt+shift) or with the "Set User Origin" button. Also, though it seemed at first that I couldn't drag anything it turned out that the object would just disappear completely while I was dragging it, no visual indication that it was there and no tracker(tracker was on). Also, while using the shift key there was no indication of mouse constraint. I just checked to be sure and Quick select doesn't seem to have any effect on user origin placement. I too found that the only fix was to restart Archicad......Strange
