Exception : There is no such object on the server at System

I try to obtain a certificate with LDAP, but i have an exception

System.Runtime.InteropServices.COMException(0x80072030): There is no such object on the server at System

My code :

Dim ldapUrl = "LDAP://annuaire.sesam-vitale.fr/cn=amo_pj.test@test.rss.fr,ou=AC-FACTURATION,ou=AC-SESAM-VITALE-2034,o=sesam-vitale,c=fr?userCertificate;binary"

Dim de As DirectoryEntry = New DirectoryEntry(ldapUrl)
de.AuthenticationType = AuthenticationTypes.None
Dim dsearch As DirectorySearcher = New DirectorySearcher(de)
dsearch.Filter = "(objectClass=*)"
Dim rs As SearchResult = dsearch.FindOne()

I have this exception at last line. I have no idea and need your help.

Thank you

(sorry for my english)

EDIT

I resolve my problem :

Public Function certificatLDAP() As X509Certificate2

        Dim certificat As X509Certificate2 = Nothing

        Dim ldapconn As LdapConnection = New LdapConnection(New LdapDirectoryIdentifier("annuaire.sesam-vitale.fr"))

        Try

            ldapconn.AuthType = AuthType.Anonymous
            ldapconn.SessionOptions.ProtocolVersion = 3


            Dim attribut(1) As String
            attribut(0) = "userCertificate;binary"

            Dim request As SearchRequest = New SearchRequest("cn=amo_pj.test@test.rss.fr,ou=AC-FACTURATION,ou=AC-SESAM-VITALE-2034,o=sesam-vitale,c=fr", "(ObjectClass=*)", Protocols.SearchScope.Base, attribut)

            Dim reponse As SearchResponse = CType(ldapconn.SendRequest(request), SearchResponse)

            For Each test As SearchResultEntry In reponse.Entries
                For Each toto As DictionaryEntry In test.Attributes
                    Dim tata As DirectoryAttribute = toto.Value
                    Dim tutu As Byte() = tata(0)
                    Return New X509Certificate2(tutu)
                Next
            Next

        Catch ex As Exception
            Throw ex
        Finally
            ldapconn.Dispose()
        End Try

        Return certificat
    End Function