RPC error when requesting a certificate

Hi, I'm trying to implement a L2TP VPN conection from a Windows XP Pro
machine it a Win 2003 Server. I set up the server as a DC and CA, and
configured the autoenrollment.

So I connect the WinXP computer to the VPN usinf normal PPTP, and it
connects fine, but the certificate doesn't get installed, even if I run
gpupdate command, and the machine is part of the domain.

I also try requesting the machine certificate using the certificates snap
in, but when trying to request it gives an error RPC server unavailable...
I've checked RPC server in the client and in the server, and it's running.

I must mention I have ISA installed in the server, but I created a rule to
let all incoming connections pass for the tests I'm running..

What can be wrong in the configuration for autoenrollment not working and
getting this RPC error when requesting the certificate??

I had the same problem and saw this on another post. Give it a try,
I'm almost certain that it will work.

ISA2004 in its "out-of-the-box" configuration blocks certificate
autoenrollment. The following ISA2004 configuration changes are
required
to allow certificate enrollment:

* The ISA2004 version must be SP1 + KB897716, SP2 (which includes
KB897716) or a later service pack. Apply updates as needed so you have
the right version.

* On the SBS2003 server, launch All Programs | Microsoft ISA Server |
ISA Server Management

* Navigate to Microsoft Internet Security and Acceleration Server 2004
|
<SBS2003 server> | Firewall Policy

* Right-click Firewall Policy and select Edit System Policy.

* Under Configuration Groups, navigate to Authentication Services |
Active Directory.

* General tab:
Enable: [checked]
Enforce strict RPC compliance: [cleared]
Click OK.

* With Firewall Policy selected, in the right pane, on the Firewall
Policy tab, locate SBS Protected Networks Access Rule. Right-click it
and select Configure RPC protocol.

* In the dialog box:
Enforce strict RPC compliance: [cleared]
Click OK.

* At the top of the right pane, click the Apply button to save the
changes and update the configuration.

* Exit the ISA MMC.

Best Regards
pferreira