Can't su from konsole

[barrera@dma.ulpgc.es]

Hi,

I can't become root using "su" command neither from konsole or xterm.
No problem if I "su" from virtual consoles.

/var/log/auth.log says:

Jan 26 14:36:55 localhost su[4993]: (pam_unix) authentication failure; 
logname=uid=1000 euid=0 tty=pts/1 ruser=barrera rhost=  user=root
Jan 26 14:36:57 localhost su[4993]: pam_authenticate: Authentication 
failure
Jan 26 14:36:57 localhost su[4993]: - pts/1 barrera:root

It seems a PAM related problem. Files in /etc/pam.d are the ones generated 
in the installation process.
I've googled around looking for help, but I can't find nothing usefull for 
me.

Any help would be appreciated. Thanks in advance.

Eduardo Rodriguez