samba - Nov 2005 - rpcclient + addform = result was WERR_ACCESS_DENIED

I am trying insert a form within a printer using samba + cups
I used the following sintaxe to insert the form:

rpcclient -L server -U user%password -c 'addform "printer"
"new_form_name"'

But I receive the following error message:
result was WERR_ACCESS_DENIED

With this user I can insert new printer, set a new driver etc, but that
operation (addform) I can't.

Someone has an idea about it ?

Thanks.

Alexandre