How do I retrieve Lotus Notes Domino directory groups and users

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VB

Using Studio 2013 VB.
I am attempting to retrieve group members from our Lotus Notes Domino directory - but I cannot get past this error: "A protocol error occurred. Failed, invalid authentication method specified." I was assuming (maybe incorrectly) that this could be done using DirectorySearcher as we do for our Active Directory.

I have tried retrieving various data with the same results. My research seems to indicate a problem with the ldapsettings but I am using the same alias and specific ldapsettings used by other in-house scripts (albeit written in perl). So the ldapsettings still might be the problem.

The line of code that fails is:

Dim result As SearchResult = searcher.FindOne

The value of searcher.Filter is (&(objectclass=dominoGroup)(cn=groupname))

Any help with errors in my code - or even suggestions to accomplish this task a better way are appreciated.

Here is my code:

dim grp as String = "mydominogroup"
Using dEntry As New DirectoryEntry("LDAP://mycompanyldapsettings")
       dEntry.Username = myadminaccount
       dEntry.Password = myadminpassword
    
       Using searcher As New DirectorySearcher(dEntry)
          searcher.Filter = String.Format("(&(objectclass=dominoGroup)(cn={0}))", grp)
          Dim result As SearchResult = searcher.FindOne <--fails here
          If result Is Nothing Then
              "report group not found"
          Else
               Dim members As Object = result.GetDirectoryEntry.Invoke("Members", Nothing)
               If members Is Nothing Then
                   "report no members found in group"
               Else
                   For Each member As Object In CType(members, IEnumerable)
                      Dim currentMember As New DirectoryEntry(member)
                      If currentMember.SchemaClassName.ToLower = "user" Then
                            Dim props As PropertyCollection = currentMember.Properties
                            "get and list the user props.someparm").Value)"
                      End If
                   Next
               End If
          End If
       End Using
    End Using