suse shutdown hangs

[Roger Searle]

Hi, suse 9.1, when I shut down this machine (and have pressed F2 to see 
the details) all the commands complete without error, as far as the 
usual second to last line of "proc umounting".  Last thing to appear 
prior to powering off is "the system will be halted immediately" however 
the system will not halt and needs to be reset.  This problem is not 
exhibited on a restart, only on a shut down, and is consistently 
exhibited. 

I don't see this behaviour on my home machine or laptop.  Is this 
related to acpi in some way?  A SuSE problem or kernel version?  Any 
clues are appreciated.

Cheers,
Roger