After upgrading the to 6.4, Splunk web would no longer start:
Starting splunk server daemon (splunkd)
... Done [ OK ]
Waiting for web server at https://127.0.0.1:8443 to be available....
WARNING: web interface does not seem to be available!
I thought it was an issue with the web.conf, so I ripped that out and it still would not start. I then removed the SSL setting in the server.conf and the server started normally. I re-added the web.conf and it again restarted fine. It is a Comodo cert (with their weird chain). The certificate works find in the web interface. We use the same for both. I though maybe it wanted a password on the key file, so I added one, that did not help. Looking at splunkd.log I see:
An additional note, verify the full.pem before trying to restart. All the certificate BEGIN and END lines must be on their own line. For some reason the cert end and key begin line were always combining in my full.pem