How can I find what is preventing a Windows computer from shutting down remotely?

We have Windows Server 2008 Service Pack 2 machines that we reboot from a Linux server using net rpc shutdown -f -r -I {ip_address} -U user%password. Usually this works fine. However, sometimes the machine gets the request and does not shutdown. I can't find anything in the logs indicating why the shutdown was cancelled. Here is the event log:

The process wininit.exe (10.18.28.223) has initiated the restart of computer server on behalf of user server\user for the following reason: Legacy API shutdown
 Reason Code: 0x80070000
 Shutdown Type: restart
 Comment: This machine will be shutdown shortly