Steps to reproduce:
1 - start a new database mongod --dbpath c:/data/bug/
2 - connect to the database and add a user to admin and disconnect
3 - restart the database with the --auth option
4 - connect to the database, switch to the admin database, and try to authorize (db.auth(...)) or try to getnonce;

You should get an error:
Thu Feb 25 19:06:08 Assertion failure getState() > 0 c:\work\buildslaves\windows_64bit_nightly\mongo\db\concurrency.h 109

Once you are in this state, it is no longer possible to auth or getnonce without restarting the server.

If you try to run a different command first, such as show users (which will give an authentication error) you can then proceed to authenticate successfully.

This is not a problem in 1.2.3.