Whirlybird,
I understand that pprune is now using different cookies, these ones expire quicker etc.
I would suggest the message you are receiving regarding logging into chat is due to not being logged into pprune, so pprune cannot log you into Digichat (different servers).
I will try and find Pprune Towers post on this and include it into the Chat FAQ.
Log into pprune first, then chat.