FC6(working 'su -') vs Centos5(failing 'su -')

[Justin W]

I've just started the process of virtualizing some of my servers into 
one machine. Right now I've been running Fedora releases for my home 
server, but keeping up with release cycles are too hard to do, 
especially when they usually coincide with me being in school. I 
successfully got Centos to run within Fedora using Xen, but now I'm 
having problems with logging in.

First, root access is allowed directly when I use virt-manager to access 
the xvc0 console. If I `su -' to my user (justin) and then `su -' again 
to root, I am prompted for the password, and once entered, I'm root again.

If I try the same technique when logging into the system as justin 
through ssh, I'm not allowed to `su -' to root. When I enter the 
password, I am returned with a "incorrect password" message. I know that 
the password being entered is correct. Following is the only logs I 
could find regarding my failed attempt to su to root (from 
/var/log/secure and /var/log/audit/audit.log)

    May 31 15:04:24 zeus su: pam_unix(su-l:auth): authentication
    failure; logname=justin uid=1000 euid=0 tty=pts/0 ruser=justin
    rhost=  user=root

    type=USER_AUTH msg=audit(1180641866.633:212): user pid=2570 uid=1000
    auid=1000 subj=user_u:system_r:unconfined_t:s0 msg='PAM:
    authentication acct=root : exe="/bin/su" (hostname=?, addr=?,
    terminal=pts/0 res=failed)'


I started digging through PAM to see if I could find anything there that 
would be blocking me. I've compared /etc/pam.d/{su,su-l,system-auth} on 
my Centos system to my Fedora 6 system and they match each other. I also 
tried adding pts/0 to /etc/securetty (though I didn't think it would 
help), and still I got nothing.

I've been thinking that I must be restricted in someway based on which 
terminal I'm logging into, but I can't find any restrictions. If you 
need any more information, I'll be happy to provide logs or 
configuration files (I just don't know what is needed).

Thanks
Justin W