Have you create the account for machine on Sme box?
Yoy have to create a machine account for the computer.But maybe you know that and have done it:)
You can do this by for example:
/usr/sbin/useradd -g 100 -G 3001 -d /dev/null -c MyPC -s /bin/false MyPC$
and for smbpasswd file the same
smbpasswd -a -m MyPC
Can you tell more about your smb.conf? Maybe there is a problem?