There are a lot of these error messages logged in splunkd.log
09-23-2010 09:31:28.062 ERROR WinEventLogChannel - subscribeToEvtChannel: Could not subscribe to Windows Event Log channel 'Microsoft-Windows-TaskScheduler/Diagnostic', 'The caller is trying to subscribe to a direct channel which is not allowed. The events for a direct channel go directly to a logfile and cannot be subscribed to.'.
09-23-2010 09:31:28.062 ERROR WinEventLogChannel - init: Init failed, unable to subscribe to Windows Event Log channel 'Microsoft-Windows-TaskScheduler/Diagnostic':
09-23-2010 09:31:28.062 ERROR WinEventLogInputProcessor - main-thread: Failed to initialize Windows Event Log 'Microsoft-Windows-TaskScheduler/Diagnostic'
Not all Windows Event log collection that appears in Manager » Data inputs » Event log collections » localhost can be subscribed. Check Microsoft Site
Also, please note, Splunk has a threshold of 63 that you can select from Available logs. Selecting more than threshold limit will cause problem. In other words, do not add all.