samba - Dec 2003 - OS X Panther and Samba 3 give me no access to a 2003 share :(

I can't mount any windows 2003 share with Samba 3 included in OS X 10.3.
I suppose that the problem is Kerberos but I just don't know how to
correct my configuration (on win2k3 and/or OS X). Here's an example of
what I get if I try to mount a share:


osxcli:~ root# mount_smbfs -U testusr1 -W TESTW2K3 //main/testusr1
/mountpt
mount_smbfs: No credentials cache found krb5_cc_get_principal
Password:
mount_smbfs: tree connect phase failed: syserr = Permission denied


File system permissions (as well as share permissions) are properly
configured and, above all, even if I try to connect with -U
administrator (with admin password) I get that kind of error :(