"Failed to join domain: Improperly formed account name"

Hi all,
               I implemented squid on RHEl5, it was working good.
I made the authentication with active directory in windows  2003 R2.
i made this possible with the help of krb5, samba, nsswitch and squid.

now we got the windows 2008 server. I made the authddn server in it.
I kept everything same on new authddn as it was in the old one.
now when i try the command  from rhel5
# kinit administrator@DDN.UPES.AC.IN
it asked for password and it runs sucessfully.

now when i try the command
# net ads join -U administrator@DDN.UPES.AC.IN
it ask for password i gave the password but it gives the follwoing error

"Failed to join domain: Improperly formed account name"

I checked everything but cant fix it can anybody please help me

thanks in advance
jatender sharma