[Samba] Failed to initialise SAM_ACCOUNT for user

[Girish]

I'm trying to create samba user accounts for users that don't have 
accounts on the machine.  I get the following error when using 
'smbpasswd -a <username>'. "Failed to initialise SAM_ACCOUNT for user <username>.  Does this user 
exist in the UNIX password database?"m I doing something wrong?  Or can you not have samba accounts if they 
don't have user accounts.I am using samba Version 3.0.14a-2thanks