Leopard shutdown problem

[soimulPatriei]

Hi all,
I have a annoying shutdown problem with my Leopard (10.5.3). Many times it does not shutdown. It issues strange message to the effect that certain applications cannot be closed. After I manually close the applications the OS exists Finder and hangs. I am forced to shutdown the system pressing the button.Next are the Console system log (for the last time when the thing happened)

Jun 11 00:00:00 Macintosh-5 newsyslog[1377]: logfile turned over
Jun 11 00:03:56 Macintosh-5 ntpd[13]: sendto(17.72.133.42) (fd=23): No route to host
Jun 11 00:05:48 Macintosh-5 loginwindow[25]: ERROR | -[ApplicationManager(AppleEventHandling) _tryQuitAllForRequestor:replyEvent:] | _tryQuitAllForRequestor - _vproc_set_global_on_demand returned error -1820028075
Jun 11 00:05:51 Macintosh-5 loginwindow[25]: ERROR | WSActivateApp | SetFrontProcess({0, 487543}) returned error -600. Unable to activate process.


Hope you can tell me how to solve the problem.
Thanks!

MacBookPro 2GHz Intel Core Duo, 2GB 667 Mhz DDR2 SDRAM
Mac OS X 10.5.3