Samba stores its data in TDB files. TDB stands for "Tiny database" and was first introduced in Samba 3.0 as a way to store information quickly and effectively.
TDB files normally are stored in 2 locations:
2. (your private directory where you smbpasswd is stored).
They sometimes break and the only way to fix them is to stop samba, move them into a suspect folder, and restart samba. Samba will recreate the files. There are 2 tools available but they only let you see what is inside the database or back the database up