When I click on Notices in the manager, the interface tries to connect to 'localhost' and all I get is a blank screen.
It says "Connected to localhost (7.6.33)" and that's it.
It used to work, but now doesn't. I'm on a Mac Mini OSX 10.12.5

Other threads on this same message board suggest that BOINC v7.6.34 for Mac was released to address this very problem.

I had a similar issue. I run Debian and found that /etc/boinc-client/gui_rpc_auth.cfg was an empty file.

file /etc/boinc-client/gui_rpc_auth.cfg
/etc/boinc-client/gui_rpc_auth.cfg: very short file (no magic)
Located the same file gui_rpc_auth.cfg in /home/myuser/ directory .

$ locate gui_rpc_auth.cfg

It contained an ASCII text, with no line terminators.

So I copied it (as root):

# cp /home/myuser/gui_rpc_auth.cfg  /etc/boinc-client/gui_rpc_auth.cfg 

And now it connects perfectly to my localhost.

(beware if you look for more "gui:rpc..." files, /var/lib/boinc-client/gui_rpc_auth.cfg is a symbolic link to /etc/boinc-client/gui_rpc_auth.cfg)

Ok I understand. It's a different problem. I also forgot that to use it as a regular user I changed permisions so that any user can launch the boincmgr

chmod 777 /usr/bin/boincmgr