It looks like the program does not see the CD at the end of the session (AHCI/IDE compatibillity driver conflict ?). When installed on HDD the problem should be gone.
If you have at least 2G (you do) of RAM you can use the LiveCD boot option Copy to RAM and check if you have a proper shutdown. In this case the commands/scripts are all read from RAM, not the LiveCD.
As last resort you have the possibillity to use the (beautifull Linux/Unix) emergency shutdown/restart without possible HDD distortion, REISUB. Hold down Ctrl-Alt-PrintScreen and push slowly one by one R E I S U B. To remember:
Raising Skinny Elephants Is Utterly Boring (RSEIUB) little different sequence, but also working. Google for details

This unlocks your keyboard, clean kills programs and flushes HDD cache from mem to disk before rebooting.
You can also put the ISO on an USB stick with the program UNetbootin (Windows and/or Linux) where you have to put fromusb at the end of the append line(s) in syslinux.cfg as in:
default menu.c32
prompt 0
menu title PCLinuxOS 2010.12 Gnome
timeout 100
label unetbootindefault
menu label Default
kernel /ubnkern
append initrd=/ubninit livecd=livecd root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=silent fromusb
label ubnentry0
menu label LiveCD
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=silent fromusb
label ubnentry1
menu label LiveCD - No Boot Splash
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=verbose fromusb
label ubnentry2
menu label Video safe mode - VESA
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=silent vesa fromusb
label ubnentry3
menu label Safe boot
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd root=/dev/rd/3 acpi=off vga=normal keyb=us vmalloc=256M noapic nolapic nopinit vesa fromusb
label ubnentry4
menu label Console
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd 3 root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=silent fromusb
label ubnentry5
menu label Copy to RAM
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd copy2ram root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=verbose
label ubnentry6
menu label Media Check
kernel /isolinux/vmlinuz
append initrd=/isolinux/initrd.gz livecd=livecd md5sum root=/dev/rd/3 apci=on vga=788 keyb=us vmalloc=256M splash=verboseNow you can boot from USB (much faster then CD)
Happy PCLos-ing
Ed