I tried installing 6.3.3 and it failed (error code 1603) due to minimum OS requirements (ie 2003 server not supported).
I have 6.2.2 currently installed on it, so it must have begun with 6.3.x.
All support for Windows Server 2003 x86 & x86_64 has been removed with Splunk 6.3.0 as stated in the docs http://docs.splunk.com/Documentation/Splunk/6.3.0/ReleaseNotes/DeprecatedFeatures#Removed_platforms
cheers, MuS
Universal Forwarder or Enterprise?
Universal forwarder on Windows 2003 SP2
I'm currently running Splunk 6.2.0.237341 on Windows 2003 SP2 with no issues. Once you go to 6.3.x its supposedly wont function. I'm going to test it this week using this old version forwarding to 6.3.3 and will let you know. This would allow you to at least still retrieve the data from the old system but use the current system for the Splunk infrastructure.