Unable to join an AD domain from Vista

Hi,

I intend to join a AD domain from a Vista Pro computer, currently in a
workgroup. Once I've filled in the account/password credentials dialog box
with a system account, I can see a pop up window with this error message:

"The following error has occured when trying to join the "yris" domain:
network path not found."

I can't see anything else in the event log...

Any hint

Oriane