Prelude is a tool that analyses the logfiles generated by another tool, for.ex. snort.
This prelude seems to have a daemon-mode where the snort-tool has to authenticate again.

I'm no expert on prelude, but it seems that you have installed snort with that exact prelude-support. Try to start that prelude-engine first. Make a user-entry for the snort-engine, and then try to start snort.

From what i can see this quickly, that should be the setup. Anyway maybe i can look into it deeper later, not right now.

Maybe this is a good reference towards your problem. Just think away the specific gentoo-commands/install references.

http://gentoo-wiki.com/HOWTO_IDS#Configuring_Prelude

Cheers.