MacOSX locks users for several reasons, for example too many login attempts.
To check and unlock these accounts withour using the GUI Workgroup Manager:
check
borg:~ root# pwpolicy -u <username> -getpolicy
Getting policy for xxx
isDisabled=0 isAdminUser=0 newPasswordRequired=0 usingHistory=0 canModifyPasswordforSelf=1 usingExpirationDate=0 usingHardExpirationDate=0 requiresAlpha=0 requiresNumeric=0 expirationDateGMT=12/31/69 hardExpireDateGMT=12/31/69 maxMinutesUntilChangePassword=0 maxMinutesUntilDisabled=0 maxMinutesOfNonUse=0 maxFailedLoginAttempts=0 minChars=0 maxChars=0 passwordCannotBeName=0 requiresMixedCase=0 requiresSymbol=0 notGuessablePattern=0 isSessionKeyAgent=0 isComputerAccount=0 adminClass=0 adminNoChangePasswords=0 adminNoSetPolicies=0 adminNoCreate=0 adminNoDelete=0 adminNoClearState=0 adminNoPromoteAdmins=0
set
borg:~ root# pwpolicy -a diradmin -u <username> -setpolicy "isDisabled=0"