WDS image_Machines are not able to join the domain using RIS account

Hi All,

we've WDS configured and working successfully for windows XP SP3 iamge.

last two week back on wards while doing image using WDS, my machines are not able to join the domain using ris account.

it is giving below error:

"The user you have specified is not permitted to join the machine to the
domain. Would you like to proceed for now an try joining a domain later?"

if i say no and enter same account and password details manually it is joining the domain. but is not happening automatically

sysprep file checked

[Identification]
    DoOldStyleDomainJoin=Yes
    JoinDomain=<domainname>
    DomainAdmin=<username>
    DomainAdminPassword=<password>

can any one help me to figure out where went wrong..

Thanks in Advance.