I'm having a bit of a problem here.
I installed the script, and it seemed to work. BUT the .disabled_for_party thing is not working for me. It says I've got a Syntax error.
Also, the "unavailable" function doesn't appear to be working either. It doesn't give an error, it just doesn't work.

I checked out the demo that you've provided, but the script is broken there as well. It opens the party interface, but all characters are available all the time. And according to Siegfried, they shouldn't be.