This sounds like a problem that we reported to IBM months ago and has been 
APARed.
The problem is that the scheduler hangs when the 'alt' key is pressed while the
ADSM scheduler session is the current session or when its icon is the 
high-lighted
icon. Guess which key is pressed when invoking the windows screen saver or lock?
The work-around is to use 'prompted' for schedmode instead of 'polling' on the
client or let the screen saver kick in automatically.