SSH: public keys for multiple users

Hey everyone,
I'm having a bit of a problem setting up SSH access for multiple
users with public (RSA) keys on my Debian box. It works fine for root
- I just have a few lines (in /root/.ssh/authorized_keys2) specifying
the keys that can login as root. But for other users (/home/user/.ssh/
authorized_keys2), that approach doesn't work - I get a "server
refused our certificate" error from Putty (ditto ssh on other Debian
boxes). Just wondering what it is I'm doing wrong - can the server not
have multiple authorized_keys2 files? Thanks in advance!

--August