Today I went to System Preferences on Mac OS X and clicked on Accounts.
Nothing happened.
The title bar showed "Loading Accounts..." but never came back with anything.
Clicking on Accounts a second time and the window just went blank.
After rebooting and trying various things, I tried
nidump passwd /
in Terminal, which revealed the "problem". An 'oracle' user had been created (by the Oracle installer) without a realname.
So I did
sudo nicl . -create /users/oracle realname "Oracle"
and it fixed the problem.
Surely Apple could make System Preferences...Accounts a little more robust than this!