I have installed kde 4.9 beta 2 on kubuntu 12.04 on amd processor system. At the shutdown time, some error is prompted however the shutdown takes place after a certain delay. This delay is not so long. I was wondering whether this is due to I/O event modification in kwin.

It can be a problem with your sound system (phonon). Ksmserver issues a shutdown notification that plays the loggout sound, if there is something wroing with your sound system the "finished" signal is never emited and ksmserver (since 4.7 something) uses a 5s timeout to continue the logout process.