Certificate Services - Web Enrollment Error

[Sektor]

Hi all,
I have a problem configuring my lab with this scenario:
- Domain A
- Domain AA as child of Domain A
- Domain AB as child of Domain A
- The users are in the domain AB
- The computer, service accout, CA are in the domain AA
- The CA is an Enterprise CA
- The Web Enrollment server is not installed on the same CA server (web
enrollment server is in the domain AA)
- The Web Enrollment server is configured to use "Windows Integrated
Authentication"

I followed all the steps described in this link
http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/security/webenroll.mspx
(configuring the web enrollment proxy for delegation).

The users are the priviliges to read/enroll/autoenroll the certificate
template.

When I try to (auto)enroll a certificate using certsrv page from the Web
Enrollment server I have this error:
The RPC Server is unavailable. 0x800706ba

Any kind of help will be greatly appreciated.
Thanks.
Sektor