Lower case/upper case problem when trying Windows XP/2003 machines with add user script like this: 
add machine script = /usr/sbin/useradd -d /dev/null -g 400 -s /bin/false %u

The issue is that there is a machine(user) name in lower case in the passwd file and in the smbpasswd file it is in upper case, so when smbd tries to set the machine password it fails. 

It works in version 3.22 without any problems. Of course, the passdb backend is smbpasswd.

Regards

Thorsten