On Windows when LogFile option is not set Zabbix agent is supposed to write log messages to Windows event log. But the
ReportEvent( system_log_handle, wType, 0, MSG_ZABBIX_MESSAGE, NULL, sizeof(*strings)-1, 0, strings, NULL);
fails with ERROR_INVALID_PARAMETER because the wNumStrings parameter is calculated incorrectly. It should be sizeof(strings) / sizeof(*strings) rather than sizeof(*strings)-1
Another problem is that agent always tries to use "Zabbix Agent" as event source event if multiple-agents startup option was specified.