I'm pretty sure it's a permissions issue, specifically, I think we need more information in /etc/pam.d/slim. Gnome-based stuff (like network manager) has changed somewhat in how it handles authorization, and slim hasn't kept up. To be perfectly honest, I had mine working correctly on my laptop for a while, but with testing other stuff I managed to break it. So now I have to enter my network password every time I connect. I intend to check it out more thoroughly when I get a chance.
For now, you can try following this guide:http://caedesnotes.wordpress.com/2010/05/05/unlock-gnome-keyring-on-login-with-slim-pam/
Just make sure that the line
session required pam_limits.so
is in whatever /etc/pam.d/slim file you use. If it's not, realtime permissions won't work with Jack or any other audio programs.