Well thats it basically, I'm running the latest version of nero (6.6.0.16). The "shut down pc after finishing" option is OFF and the system doesn't shut down properly it just shuts down as if it would when you press the power button on your pc. The problem is contained to multisession CD-r's, multisession DVD+r & DVD+RW work fine.
this probably won't help, but it's worth a go.. ..post LAST section of your Nero log, which is in c:\program files\ahead\nero\nerohistory.log, but DO NOT post your serial number which usually begins with '1A21' or similar