Problem with CertEnroll library and request with Subject Alternative Names created with certreq

I have generated a certificate request with SANs using an inf file like this:

[Version] 
Signature="$Windows NT$"
[NewRequest]
Subject = "CN=someone,DC=acme,DC=com"
KeyLength = 2048
[Extensions]
2.5.29.17 = "{text}"
_continue_ = "dn=CN=someoneelse,DC=acme,DC=com"

If I submit the request, the certificate includes the SAN correctly.

My problem is that I need to read the request file programmatically:

using CERTENROLLLib;
using System;

class Program {

    const string RequestString = @"-----BEGIN NEW CERTIFICATE REQUEST-----...";

    static void Main(string[] args) {
        CX509CertificateRequestPkcs10 request = new CX509CertificateRequestPkcs10();
        request.InitializeDecode(RequestString, EncodingType.XCN_CRYPT_STRING_BASE64_ANY);
        Console.WriteLine("Subject: {0}", request.Subject.Name);
        foreach (IX509Extension ext in request.X509Extensions) {
            if (ext.ObjectId.Name == CERTENROLL_OBJECTID.XCN_OID_SUBJECT_ALT_NAME2) {
                CX509ExtensionAlternativeNames extensionAlternativeNames = new CX509ExtensionAlternativeNames();
                // Following line fails with this COMException:
                // The requested property value is empty. (Exception from HRESULT: 0x80094004)
                string rawData = ext.RawData[EncodingType.XCN_CRYPT_STRING_BASE64];
                extensionAlternativeNames.InitializeDecode(EncodingType.XCN_CRYPT_STRING_BASE64, rawData);
                foreach (CAlternativeName alternativeName in extensionAlternativeNames.AlternativeNames) {
                    Console.WriteLine("SAN: {0}", alternativeName.strValue);
                }
            }
        }
    }

}

The same code works perfectly if I generate a request with SANs using openssl, for example.

Any hints?

Thanks,
Paolo 

Paolo Tedesco - http://cern.ch/idm